A/N: If you recognize it, I don't own it. This fic is heavily, heavily based on Jim Brickman's song "By Heart," which is definitely one of my favorite songs ever. It's not required listening for this fic, but if you ever feel like listening to a great song, definitely look it up.

The planet Nashira-2 is a fictional (as far as I know) planet orbiting a real star, Nashira. I don't know of any star name that means "bad wolf" so I used one that means "she brings good news" instead. I thought it was fitting.

Want to help me beta fics like this? Check my profile and send me a PM!

By Heart

"How long are you going to stay with me?" That was his favorite question, his way of saying three little words that Rose knew he couldn't bear to speak. She smiled, snuggling into his warm embrace, happy just to be in his arms.

"Forever. I'm never going to leave you."

She lay on his pinstriped shoulder and felt him sigh. "Rose, I'm… forever is… we…" He struggled so much to say it, because saying it would make it so much more real. I'm terrified of losing you. Forever is too short, especially for a human. We won't have more than a few decades and I can't bear for that to end. If he didn't say it, maybe they could pretend that their few decades would last an eternity.

"I know," Rose said. She leaned up and kissed his cheek. "I know. I don't care. I mean it; I'll always be with you, forever and ever."

The Doctor said nothing, but held her closer, as if he never wanted to let her go.

And now… now she was gone, trapped forever in a world parallel to this one. And here he was, standing in the TARDIS, burning up a sun because he thought it would help him say goodbye.

He could see her. She had come to his call; she was sitting on a rock, facing out to sea, sitting on a beach which looked like the middle of nowhere.

"Rose?"

Her head snapped up and around. She smiled – as if she had never doubted his ability to do the impossible. She stood up smoothly, circling the rock and coming toward him.

"You came."

"I'm not really here. Just an image. There was one little rip left in the universe."

"Too small for you to come through?"

"Too small for anyone to fit through."

Rose was crying, crying for both of them because he was too heartbroken to do it for himself. He took a deep, steadying breath.

"How long can you stay?"

"Not long. A few minutes?"

"I love you."

"I know," the Doctor admitted. "I know. I…"

"No." Rose bowed her head briefly. "No, don't say it. You can't."

The Doctor said nothing. She was right. Keeping those words to himself was his only chance at surviving her loss. She had always cared for him more than herself – exactly the same way he had cared for her.

"I wish I could stay longer," he said instead. Rose sniffed and tried to rub the tears from her eyes. She had no success. The Doctor wished he could reach out and brush them away.

"Where's the rip?" she asked, her voice straining to maintain some normality through her tears. The Doctor gestured to his right, outlining the rift with his hands. It was only the size of a mail slot – too small. Rose reached up and unfastened her necklace – the rather plain pendant he had given her. She pressed it to her lips and wrapped her fingers around the chain. Then she stuck her hand through the rip, and suddenly she was in two universes at once; simultaneously on the TARDIS and stuck on a forsaken beach in the middle of Scandinavia.

"Take it," she pleaded.

"Rose – " But he reached up and took the pendant from her, careful not to let his fingers brush hers. If they touched, he wouldn't be able to resist; he'd try to pull her through, into the TARDIS with him, and both their universes would die so that they could have another few seconds together. Rose was being similarly cautious, thinking similar thoughts, and she pulled her hand back once the chain was untangled from her fingers. "Thank you," he said simply, his voice laden with all the sorrow he could not hope to express properly.

"Ask me, Doctor. One more time."

And now he looked at her in pain. How could she ask that of him? How could she, when they were about to be separated forever?

"Please," he said, unable to articulate the rest. Please don't make me do this; I'll suffer enough as it is.

"One more time. For me?"

And he acquiesced, because he couldn't bear to disappoint her. He met her eyes – those hazel eyes he so adored. "How long will you stay with me?"

Rose smiled through her tears, through her running mascara and smudged eyeliner. "Forever. Even if we're worlds apart, I'll find my way back to you. And I'll stay with you forever." She was rubbing at her eyes with her sleeve, trying to rub away the tears, oblivious to the fact that she now had dark stains across her cheeks. It only made her more beautiful to him.

The TARDIS chimed softly in his ear. The connection was already closing. The Doctor said, "Goodbye, Rose." And she faded away, as if she had never been there – except that her pendant still dangled from his fingers. He slid it into his pocket, hung his head, turned toward the console. And that was that. She was gone, and he was alone. Forever had been much too short.

Months passed. Years passed. Decades passed into centuries. The Doctor travelled on, solving problems, stopping genocides, saving worlds. He did it for her, for the one who had promised him forever. He had found her watch, sitting on her bedside table. He had stopped it, smashed the mechanism so that it would always display the date and time he had seen her last. She couldn't stay with him forever, but he could remember her. He could remember her until his dying breath – in that way, she would be with him.

And then he found her again.

It was on the planet Nashira-2 that he met her. The Doctor had seen a flash of familiar blond hair and had followed it, like a lost puppy trailing after its owner. She'd ducked into an alley and he had turned into it as well, automatically, only to be confronted by her face – so achingly familiar, with beautiful hazel eyes and a mischievous smile, the tip of her tongue visible between her teeth.

"So why ya followin' me, then, mate?" She looked him up and down while his heart quietly broke. "No, 'ang on – d'ya go by the name Doctor, any chance?"

"That's – that's me," he agreed jovially, swinging back into carefree happiness when the pain became too much to bear. All that pain curled up on itself within his hearts, leaving his lips free to smile their broadest and his eyes to sparkle and outshine the stars.

"Good, I thought you'd be comin'! You still 'ave my necklace, any chance?" She glanced curiously at his pocket. The Doctor reached into it and produced her necklace – the one Rose had given him.

"Who are you?"

She'd reached out to take the necklace, looking for all the world as casual as if it was of course hers. "Lily," she said. "Lily Taylor. I'm twenty years old and you are late." She took the necklace and fastened it casually around her neck. She didn't fumble with the clasp, as if it were a new necklace; she was familiar with it. The Doctor knew for a fact it was one-of-a-kind. It hung there, at her throat, like it had always been meant to hang there. The Doctor looked her over, Rose's words echoing through his mind. She had a different name, but she acted the same – she had been born on a different planet, but her accent was the same. She didn't seem to recognize him, but she knew who he was. "So, c'mon then? TARDIS around anywhere?"

"Wait." Lily Taylor stopped walking away. She half turned to look over her shoulder at him, raising one eyebrow as if to ask him why he was suddenly reluctant. "How long are you going to stay with me?" His voice was barely a whisper, and his eyes pleaded with her to give him the answer that would prove it. He didn't know what it was, only that he would know if it was true. She turned back to him, took his hand and smiled gently at him, Rose's smile, just like she always had – telling him that everything was okay and always would be. Telling him she understood what he was saying, and what he couldn't say.

"Forever," she promised without missing a beat. Lily Taylor flashed him that cheeky grin he had always loved so much. "I found my way back to you."

The Doctor said nothing, just wrapped his arms around her and held her as if he would never let her go.

Maybe, just maybe… he wouldn't have to.

And even if we're worlds apart, I'll find my way back to you by heart.