Notes: I decided to split this fill in half, more or less, because it's starting to get really, really long and I didn't really fancy crushing everyone with a giant fic of text. So, uh, here's the first part.
Title: How a Heart Breaks
Part: 1 / 2 (?)
Fandom: Thor
Pairing: eventual Thor/Loki ; implied/one-sided(?) Jane/Thor
Rating: pg13
Words: 5427 words
Beta: elliott ashes
Prompt: AU where Thor and Loki are soulmates or bonded or equivalent. It could be official, intentional, accidental, or maybe they don't even know. But when Thor is exiled and begins to fall for Jane, it starts tearing at the bond, driving Loki slowly mad. [ original post here ]
Disclaimer: It's not mine. The character belong to Marvel and the studio which produces the movies; I'm just playing in the sandbox. I make nothing from this.

How a Heart Breaks, Part 1

Thor had been banished. That... hadn't exactly been part of his plan. But he had to do something or else things wouldn't turn out well. Thor couldn't take the throne, not when he was arrogant and unwilling to think through the consequences of his actions or anything. He was hot-headed and brash and violent, not very likely to listen to reason.

Maybe the exile on Midgard would change him. He could always hope.

And he would keep to himself the fact that his heart felt like it had been torn apart.

Loki didn't understand it. This was for the best. That's what he always told himself over and over again, but each time it sounded less sure and sincere than the last one.

But that didn't put a stop to the dull ache that had settled into his chest, right where his heart was. It was a heavy feeling too, like something was pulling him down constantly. Could it have something to do with what he was? He had no idea.

Still, the way his limbs felt heavy was something new. None of the – sometimes – creative punishments that he'd received for his mischief as a child compared to how he felt right then. It was as though a huge weight had been dropped on him or that he was trying to move through water, his movements felt sluggish and uncoordinated. He didn't like it.

rigga had looked at him, concerned, the moment that they entered the citadel. She'd glanced at Odin briefly before her eyes returned to Loki and she quickly made her way over to him, her stride determined so that she could catch him before he could, presumably, disappear somewhere.

She quickly fell into step beside her son, sparing Sif and the Warriors Three a brief glance. Fandral was leaning heavily against Volstagg, but other than that, the four of them seemed to be in fine health.

It was the absence of her eldest son that worried her most.

"Loki."

"Why didn't you tell me?"

She let out a small sigh, "I never wanted to burden you with that knowledge. You are my son – our son – Loki, your father and I love you. We simply wanted to protect you."

He gave a snort, "Of course. You couldn't have a Frost Giant sitting on the throne of Asgard. That is why you always favoured–"

"I love both you and Thor equally," Frigga replied, tone firm but with a hint of reprimand in it. "You are both my sons, whether that relation is by blood or not. We have raised you all these years, Loki, and we have loved you. That makes you our son – not your blood, whatever it might be."

Loki gave no response, but Frigga knew better than to think that the issue would be dropped. He had always twisted words, misjudged their meaning.

"How do you feel?"

"Mother – what? I do not understand."

She sighed, "Do not lie to me, Loki. I am your mother, I know when there is something that is bothering you."

"It's nothing."

Frigga frowned at that; she knew that Loki would be dishonest, whatever was hurting him, or worrying him, he would lie about it. She could press the issue, but there was the chance that he'd just lie as he usually did.

"Loki, if something is bothering you, than I want you to be able to speak with me of it," Frigga said softly. "Promise me that if it gets worse, you will come to me about it."

There was a hard look in her eyes when Loki looked at her and her voice was hard as she repeated herself.

"Promise me."

He couldn't see a way around it. Frigga was as stubborn as he was.

"I will." He paused, noting the way her lips pulled down a little at that. "I promise, mother."

Frigga smiled at him, warm and full of love and it was so hard to believe that she didn't really love him as she did Thor. His heart gave a painful throb at that and his head felt a little cloudy.

They stopped in front of his rooms and Frigga reached out, giving his arm a comforting squeeze to go with her warm smile, "Go and rest, Loki. It has been a long day for all of us. We may speak more on this in the morning."

He nodded, feeling as though cotton had been shoved down his throat, "If that is what you wish, mother. Good-night."

"Good-night, my son. Sleep well."

With a small flourish of her dress, Frigga swept away down the hall; most likely going to comfort or speak with her husband. Loki still felt betrayed by Odin, but Frigga... it was harder to doubt her feelings, she was always so honest and straight-forward. She had always loved him and comforted him whenever he needed it as a child. No matter what could be said about his blood, she was his mother.

He entered his room and stripped out of his armour, tossing it aside almost carelessly. When he was left in only his thin tunic, he flopped back onto his bed and stared at his hand. He could still see the blue flesh, how it had turned when that giant had grabbed him...

The anger still burned inside of him. The single unanswered question bounced around his head as he struggled to find an answer to it.

Why?

Why had they lied to him? Why had Odin taken him in the first place? Why adopt him? Why? Why? Why?

He couldn't make sense of any of it and he eventually fell asleep mulling over all of those questions and just what could be wrong with him. For the first time in many years, Loki felt afraid as to what the answers might be.

That night, his sleep was restless.

– – –

One simple glamour later the next morning, and he looked completely awake and healthy. But he didn't feel like it.

Loki felt tired and sore, like he'd just suffered through one of Thor's brutal training sessions without a respite and then slept on a bed of rocks. His muscles protested every little movement almost violently and it took a considerable amount of willpower – and a little bit of magic – to hide the way his hands shook.

When he'd looked in the mirror that morning, he'd been surprised by what he saw. He looked much paler than he usually did and there were the beginnings of dark circles under his eyes.

He picked at his food, appetite virtually non-existent.

Over the breakfast table, Frigga gave him concerned glances and they weighed on him. The feeling of suffocating weight from the day before hadn't lessened any and, in fact, it felt worse; like he was deep underwater and unable to pull himself to the surface to breathe.

Further down the table, Sif was giving him a dark, searching look. Clearly, she felt that he was in some way responsible for Thor's banishment – and technically he was, but he'd never admit that to her – and she wasn't going to forgive him for that anytime soon. He was used to that; Sif was usually mistrustful of him whenever something went wrong, he was always involved in that sort of thing somehow.

At that moment, though, he wished that Thor was there. Despite being something of a lumbering oaf, Thor always managed to cheer him up and make him feel better just by being there.

He never understood that himself and he didn't care to figure it out; it wasn't important.

Odin's presence was notable in its absence. The Allfather had been feeling weary as of late; he would probably be entering the Odinsleep sometime in the very near future.

The thought nearly made Loki's stomach drop out. With Thor gone and the length of the Odinsleep undetermined, it meant that, in all likelihood, the crown would fall to him in the intermediary period. Something about that... it didn't feel right to him.

With blood pounding in his head and making the headache he felt coming on worse, Loki quickly stood up.

And blinked back the dizziness at that action.

"Please, excuse me."

It took much more control than he felt to quickly leave the dining hall without stumbling over legs that felt unsteady under him. He had no idea of what was going on, what was making him feel ill and that irritated him; he wasn't used to being in the dark about anything.

Perhaps it was the cold of Jotenheim still lingering in his flesh, but that was ridiculous and he quickly dismissed it.

A spell of some sort perhaps? That seemed the most likely explanation. He would have to look into it, do some research to see if there was some way to counteract it.

Course decided on, Loki quickly switched his destination from his chambers to the library. It might take him all day, but he was determined to figure out what spell had been cast on him before it was too late. He couldn't go on like this, feeling as though he was slowly being torn apart from the inside and with his heart having been torn in two.

Despite this determination, there was a niggling little voice in the back of his mind which told him that it wasn't so simple as that. He pushed it aside.

Loki didn't want to think about the other possibilities.

– – –

The rest of the day passed in slow motion and Loki made no progress. All he got for his trouble was a rapidly worsening headache, burning eyes, and slightly blurred vision. Stacked on the table surrounding him were multiple spell books, each one more complicated than the one before it. He'd made no progress whatsoever.

Loki had checked almost every strand of magic that he could think of, but none offered the answers he sought. No spell matched or could explain his symptoms; the effects were usually more sudden and even with a delayed effect wouldn't cause this. Loki had studied and mastered magic for years, but he'd never come across something like this.

What did it mean? Loki wondered. Maybe an illness?

Laying his head down on the page in front of him, Loki closed his eyes and took several deep breaths. If nothing else, the throbbing in his head grew more insistent. An illness would explain his symptoms and why they were getting progressively worse.

It was late in the evening, though, and it was hard to concentrate. The words had started running together in front of his eyes and towards the end of his reading, he'd realized too late that he'd been reading the same passage over and over again. He'd missed lunch in favour of pursuing his research and it was far too late to bother with dinner. Besides that, he wasn't hungry; he'd lost his appetite around the same time that he'd started feeling sick.

And if he was really sick, then...

He wished Thor was there.

That thought made Loki flush and his heart flutter wildly, like a butterfly's wings. He wasn't sure of where the thought had come from. Thor wasn't his brother – Loki was a monster, not deserving of that position – so why should he miss him?

No matter how many times Thor had nursed him back to health, sat at his bedside while he was injured, kept him company while he recovered... all that was gone now. He had no right to it; not any longer.

Opening his eyes, he stared blankly at the pages of the book before him. It was a complicated and difficult spell, one which he'd mastered years ago. The words, which had once been so clear and concise to him, now bled together; the ink and symbols blurring into a incomprehensible mess.

It made his headache worse.

Pushing himself back up into a sitting position, Loki noted how pale his hands looked. They were also trembling horribly as he did so. When he held them up to his face, he noted how they shook; he couldn't stop the shaking.

It was worrying. Loki wondered if he should see a healer about this or if he should continue to try and figure out the answer on his own. If it had to do with his biology... he'd rather not have anyone else know about it. He was ostracized and looked down upon enough as it was, he didn't need to add to that.

Loki didn't understand it. He'd been alone and often excluded for so long that it shouldn't have mattered if there was one more – better – reason for him to be pushed aside.

He was the monster that parents told their children about at night, the one that gave them nightmares. Maybe it would be better for himself if he just disappeared. No one would miss him, no one would worry about him.

All of that was true, with Thor gone.

Glaring at the book, he slammed it closed. His brother should not have been clouding his thoughts like that, nor should his name have caused his heart to give a violent lurch. Loki let out a gasp, hand clasping over his chest as the pain radiated outwards and burned.

It felt as though someone had lit a fire in his chest, with his heart being at the centre of it all. Loki felt his blood run cold and then hot. Squeezing his eyes closed, he murmured a quick spell to lessen the pain, but it didn't make it any better. If anything, it made it worse.

Why? Why does it hurt? I want it to stop...He would have cursed Thor out if it wasn't for the thought that the mere thought of him made Loki feel as though a part of himself had been torn away and killed.

That was what it felt like. It was as though a part of him had died.

It was the last coherent thought that he had that night. The next thing that Loki remembered was the morning light streaming in across his face as he was sprawled across the cover of the book he'd been studying the night before. His cheek stuck to the cover and his body was stiff and sore, more so than the day before.

For Loki, that was the first sign that something was terribly wrong. It was also the first major sign that he ignored.

– – –

The dizzy spells were harder to deal with and hide then his rather sickly appearance. His head spun whenever he stood up too suddenly or turned too quickly and his vision spun as well, making him very unsteady on his feet. The headache had become his constant companion and seemed to be getting worse instead of better, his appetite was decreasing too.

Loki wasn't sure of what it meant. It reminded him of when he'd been younger and he'd fallen ill for days on end; Thor had always recovered quickly in a day or two. Of the two of them, Thor had always been the stronger one; at least physically. But he never forgot his younger brother.

Brother. Loki didn't think he was deserving of that word any longer. He was nothing like Thor, they were not brothers. He was worth nothing to him.

And that tore apart his already fragile heart even more than before. It felt a little like his heart had been placed on one of those blocks that the cooks used for the chopping of meat in the kitchens. But the cuts weren't clean, they were ragged and felt more as though they'd been torn instead of cut. The pain was... indescribable.

He had a splitting headache to go with the pain in his chest, which made it nearly impossible to concentrate on the research he needed to do. No matter how hard he tried, he couldn't make it abate in the slightest.

Frigga found him in the library late the morning after he'd collapsed from exhaustion – or at least, he told himself that was what had caused it. Loki hadn't heard her enter.

"How are you feeling this morning?"

Her softly spoken question nearly made him jump. Or at least, he would have if he didn't feel so sluggish. Instead, he turned slowly to face her, joints aching and limbs sore.

"I... feel fine." It was a lie and Loki knew that Frigga would see through it in an instant.

Loki's head was pounding and his tongue felt slow, as did his mind. The trembling in his hands had abated somewhat, but there was still an almost imperceptible tremor to them when he held them up. And he felt cold, like there was a constant chill hovering about him. That was a new symptom.

Frigga frowned, her eyes narrowed; she'd caught the way his hands were shaking. "Please do not lie to me, Loki."

She gracefully folded herself down onto the bench next to him, letting one hand come to rest on his forearm, "Clearly something is troubling you. Please, you do not have to bear that burden alone."

I've always been alone. Thor left me.

Again with those thoughts of Thor. They always intruded, like snakes winding their way through his carefully maintained defences and undermining it. Loki felt like he was quickly become undone and there were no answers; his mind had become his own worst enemy in the span of only a short few days. All of his thoughts came back to Thor, how he'd left him and how he missed him.

"Does what is ailing you have to do with Thor's banishment?"

Loki stared at her in shock, blinking slowly. How could she have known? Was he really growing to be that transparent?

She gave him a small, warm smile, "I am your mother, Loki. I know you all too well; you cannot fool me so easily."

He sighed, shoulders slumping. "... it might. I really don't see how that has anything to do with my health."

"Despite what you may think, Loki, Thor is your brother. It is only natural to feel sadness now that he's no longer with us in Asgard. But you must not lose hope that he will return to us."

That made him freeze and he stared at his hands, his stomach doing odd little flips. I am the reason why he was banished in the first place.

Frigga drew him into a gentle embrace, her arms sliding easily around his shoulders just like they'd done countless times before when he'd been a child. She stroked his hair gently and pressed her lips to his temple in that same comforting way of hers that never seemed to change no matter how much time had passed.

Her question hung heavily in the air, and Loki mulled it over silently as he tried to come up with an answer. There was always the possibility that she knew – because Frigga always knew, somehow. Perhaps it was that mother's instinct of hers, she'd always seemed to know when he needed her as a child and now she'd comfort him when he felt down.

The silence hung between them for a long stretch of minutes, with Loki fighting with himself about whether or not to just admit to her what was wrong with him.

Much like those thoughts of his brother, Loki found the words tumbling out past his lips before he could connect them to any potential consequences.

"I feel... faint, as though something important is missing."

– – –

Frigga had always felt that things would turn out this way. Whether it was simply her mother's instinct or just intuition, Frigga had known that her two sons were simply meant to be... ever since Loki was placed in her arms, she knew.

When a young Thor had waddled his way over to her to behold his new baby brother for the first time, Frigga had seen the connection form almost instantly between them. It was a golden thread that snapped into visibility for a few brief seconds before it disappeared.

The two of them were bonded together – never meant to be apart or be with anyone else.

But what Loki had told her was of concern. The feeling of being faint and that something was missing was normal, considering the circumstances, but the other symptoms made things a little more complicated then she'd first thought.

The bond was tearing. If something wasn't done, then it would result in Loki's death.

And she could not bear for that fate to befall her youngest son, especially since she had no idea how Loki's death would affect Thor. With bonded pairs being so rare, there was no precedent.

However, no matter what, the consequences could not be good. That much she did know.

Frigga made her decision to watch Thor's time on Midgard much closer than she had before, there had to be a reason for why the bond was being torn. In the meantime, she pressed her lips to Loki's temple and gave him her best comforting, motherly smile.

"Oh, Loki," she murmured softly. "I had always known of your connection to Thor... but I never thought that this would happen."

His head snapped up at that. Frigga took in his appearance, the dark circles under his eyes and how pale his skin was; Loki looked as though he was suffering from an illness. And she had no idea what to do for him.

That tore her in two.

"What do you mean?"

"I had planned to tell you soon, once Thor had been crowned, but as things have played out... now is as good a time as any." Frigga let out a sigh, letting her head rest on Loki's shoulder.

"Mother–"

"Thor is your bonded – your other half, Loki."

– – –

Even though she had told Loki of his connection to his brother, Frigga knew that there was more to it than that. After all, bonded couples were a rarity in Asgard. Information on them was scattered and fragmented; in short, there was very little information on them. Not even she knew much of them or what it meant to be one half of the pair.

She, personally, was not one, but she had always known that Thor and Loki shared a special connection. It had been Heimdall – watching the young children for his king and queen – who had told her exactly what it was.

"It is rare to see a bonded pair, I can only hope that their destiny will not end in tragedy."

And, of course, as it stood right then, she was truly almost powerless to do anything.

Frigga had suspicions, of course, that perhaps Loki's health's steady decline was due to Thor's slowly burgeoning relationship with that young mortal – Jane, if she remembered correctly. After all, Loki had seemed... more or less fine after Thor was banished, just minus an important part of himself.

She frowned, observing Thor from her place at her resting husband's side. He'd fallen into the Odinsleep shortly after Thor's banishment, the stress had finally gotten to him at last and he'd simply collapsed. Frigga couldn't help but feel that perhaps this was for the best.

After all, while her husband was wise and she loved him dearly, there were certain situations in which he lacked the necessary tact.

He'd never known that Thor and Loki were bonded. Frigga had never told him and he had never figured it out. If nothing else, she thought that she should count that as a blessing. There were times even she could not predict how her husband might react to certain developments.

As for the others, she would leave the choice of informing them of this development to her sons. It was their lives, after all, and she did not feel that meddling in them would be in their best interest.

But perhaps she would pay Thor a little visit.

– – –

"I would speak with you, Loki."

Turning around, Loki was mildly surprised to find Sif standing in front of him with her hands on her hips and a determined set to her jaw. She'd caught him before he could slip away from the table with their friends – he had barely touched his food and he'd been avoiding the dining chamber for the past few days – and he knew she'd been wanting to do this for a while.

"What is it?"

"You're plotting something, I know you are." She stepped forward and Loki was ashamed to admit that he flinched away from her.

"I am not plotting any–"

"Do not lie about this. I know you, Loki, and I know that you always have some plot or scheme afoot. What is it this time?" Sif narrowed her eyes, watching him closely with a warrior's keen eye. "You have hardly been in public since Thor's banishment and you spend all that time holed up in your chambers or the library. So what do you have planned now?"

Loki could feel his heart pounding wildly in his chest. Something didn't feel right. He felt light-headed and dizzy and his vision was blurring at the edges. Trying to blink it back didn't work and it was only his own sheer force of will which kept him on his feet.

"Nothing."

She scoffed at that, stepping forward and backing him further into the corner. Loki shot a quick glance over her shoulder and felt a little dismayed that the others were only giving the two of them wary glances. At that moment, he couldn't tell if they agreed with Sif or were just – wisely – choosing to stay out of this little conflict.

"If I find that you have had anything to do with this or if anything else were to happen to Thor, I will make sure that you will not escape unpunished." Sif tightened her hands into fists and glared straight at Loki, refusing to avert her eyes.

It was unnerving.

True, he'd always known that Sif was the most suspicious, that she harboured some feelings for Thor that ran beyond mere friendship; however he had never expected nor anticipated this. But then again, what made playing pranks on Sif so rewarding – especially as a child – was the unpredictability of her reactions.

But he could have probably done without this one. Loki could feel his heart pumping sluggishly and his muscles were trembling with the effort of keeping him on his feet. Sweat was forming on his skin and the dizziness was suddenly much worse.

It felt like the ground had been pulled out from under him. The nausea felt worse. His vision was spinning and blurring out into black dots.

He had to leave.

Loki wasn't sure how he did it, but he managed to stumble out of the room. Then he collapsed in a faint.

After that, he couldn't remember anything.

– – –

Sif had, at first, been convinced that Loki was plotting something. It wouldn't have been the first time that he'd manipulate events or play the weak card in order to get the results he was hoping for. She'd seen variations of it all before and she refused to fall for any more of his tricks.

It had... bothered her that none of the others had never been particularly suspicious of Loki, always taking his words to them at face value. They trusted him.

And it burned her stomach and tore at her heart to know that Thor placed far more trust in his trickster brother than he did in her. She had fought tooth and nail to be recognized as a warrior and, dare she believe it, Thor's equal. In the end, all she wanted was for him to recognize her as being more than a battle companion.

She loved him. To the point where it felt that her heart might have burst.

But his brother had always come first in Thor's thoughts. Loki was always more important to him.

There was just no way that she could compete with that. Even Loki, of all people, seemed to have something of a soft spot for his brother.

And she was always suspicious of that. Sif was well-aware that Loki wasn't above using others' feelings for him against them. It was entirely possible that Loki might have orchestrated everything that had happened to lead to Thor's banishment to meet his own ends – whatever those might have been.

However, she certainly hadn't expected to find him collapsed in the hall outside of the dining hall.

Sif stared at him for a moment, torn very briefly between just leaving him there or kicking him to make sure he wasn't simply faking it. It wouldn't be the first time.

Approaching the seemingly unconscious trickster warily, Sif nudged his side with her foot. He didn't so much as twitch in response. She tried again, harder this time. Again, no response.

A tiny twinge of worry wiggled its way into her stomach and she crushed it back down. She was not worried about Loki, not one bit. It would be stupid and unsightly. Instead, she quickly knelt down at his side and grasped his shoulder – he'd fallen in a messy heap of limbs; that is so unlike him, Sif thought – and shook it, hard.

"Loki. This is no time for games."

He said nothing. Loki didn't so much as move.

"I will fetch your mother if you do not stop this childish display."

Still nothing.

And that was ultimately what had Sif admit that yes, she was worried for Loki.

"Guards! Guards!"

Two palace guards swept into the room, Sif quickly stood and gestured at the unconscious Loki, "He collapsed, please hurry and take him to his chambers. And fetch her majesty as well."

One of the guards gave a sharp nod before sweeping off to locate the queen while the other stooped down, sliding an arm under Loki's knees and another under his shoulders. He gave a curt nod to Sif before he, too, left to take the unconscious prince to his chambers.

And once again, Sif was left alone to her thoughts.

She crossed her arms and frowned, then quickly returned to the dining hall to rejoin her companions. It probably would be for the best that they hear the latest news from her rather than from the gossip of the servants and other citizens of Asgard.

Hogun was standing just inside of the door, his arms crossed and an almost serene expression on his face. But his eyes were furrowed; it was likely that he'd heard the entire exchange.

"Loki has collapsed?"

Sif nodded, "Yes. I don't know whether or not this is part of some plan of his or–"

"I think not," Fandral interrupted. "He might be crafty, but I doubt that he would put his appearance and reputation on the line for something so simple as a mere prank."

She shot him a look and Fandral shrank back. "All of you are far too trusting of him. You never do believe him guilty of any wrong where Thor is concerned. I remain convinced that this is simply another of his plans, although I have no idea of what his ultimate goal is."

"No."

All of them whirled to face Hogun, who was staring at the wall. "What?"

"I do not think that this was a part of Loki's plan – if he had one at all, ultimately."

Volstagg nodded, "I must agree with Hogun. Loki has not touched any food since our return and... well, he did not look particularly well upon Thor's banishment either."

"None of you agree with me." Sif frowned, her hands tightening into fists again before letting out a heavy sigh and relaxing them. "And for once... I agree with all of you."

– – –

Frigga gently brushed back the bangs of her youngest son, taking the cloth from the small basin on the bedside table and wringing it out before placing it back on Loki's forehead. The fever was a weak one, but it would grow stronger over time.

She let out a heavy sigh as she settled back into her sleep and watched Loki as he lay in sleep. Frigga had been to speak with Heimdall, of course, since he was much older than even she and Odin and wise in such matters. It had been him who had filled her in on the more intimate details of what it meant to be a part of a bonded pair and what she should expect in the future.

"If Thor does not return and take Loki for his consort, then Loki will die. It is that simple. As for Thor, he will gradually grow weaker. It is very unlikely that one will survive the other... although, given that neither was aware of the connection, there is a chance that this might happen."

It was a difficult time for Frigga. She knew that she had to keep projecting an image of strength, for the Frost Giants had been simmering after Thor's little excursion into their territory and were, quite likely, longing for blood.

And with Thor having been banished, Loki unconscious, and Odin in the Odinsleep, well, they would seize any chance that they could. At that moment in time, they could only wait and see what would happen next.

More importantly, Frigga could only pray for Thor's swift return. Everything Odin did was for a reason. She just had to wait until Thor could figure out what that was.