"I'd rather have you in my life even as a brother than not at all—"

"And I'm supposed to sit by while you date boys, fall in love with someone else, get married...?" His voice tightened. "And meanwhile, I'll die a little more every day, watching."

"No. You won't care by then."

[...]

"I love you, and I will love you until I die, and if there's a life after that, I'll love you."

City of Glass Pg. 331 American edition

Disclaimer: I don't own anything Mortal Instruments related.

AN: So I thought about the above passage from City of Glass and wondered, what if they never found out they weren't siblings? What if Valentine was dead and they still couldn't be together?

Voila! Clary getting married to someone else popped into my head.

It wasn't that he knew it couldn't happen, he just thought it wouldn't. Clary, the one woman Jace ever loved, was getting married—that afternoon. And what hurt the most, what he couldn't comprehend, was why she was going through with it.

Just the night before they had made love again, Clary claiming that she would call off the wedding and run away with him. Jace was prepared to give up his life of demon hunting; it would be worth it if he could just be with Clary. He had nothing to lose, and everything to gain. Despite being her brother, his feelings remained unmoved, solid.

But fate was cruel, it always had been, and Clary called him early the next morning. She said it was a mistake; she loved her fiancé, and couldn't bear to hurt her mother so badly. She hung up on him swiftly, not letting him get out a retort. She broke his heart further into a million pieces.

As much as he had tried over the years to get over her, to date other women and distract himself from the truth, nothing had changed his feelings. Clary was the love of his life, now and forever.

He sighed and rolled out of bed. Despite his complete objection to her wedding, Jace was going to be there. He would put on a brave face, smile with all the other guests, and die even more when she agreed to her vows. Besides, Isabelle would kill him if he ditched her. She was his date, in very loose terms, and was the only one who would probably keep him in line.

Jace needed a shave badly. He went into his small bathroom in the Institute, the same one he had been using since he was ten. The only thing that was different after all the years was the hair brush that Clary had forgotten from the previous night. He picked it up and took in the familiar scent of Clary.

Memories flooded him instantly. He could remember the first night they had been together, rushed and quiet, and very, very selfish of him. She had been trying to tell him how they could not be together—they were siblings! He had pushed her until she said yes, just once.

It had been unbelievable, being so connected to her, and even after she promised that it would only be once, he had managed to get her again, and again. Even after she had met someone else, fallen for someone else, he managed to bring her back into his warm, inviting bed. Jace punished himself every time for his selfish acts, fighting demons that were well beyond his own capabilities, almost dying on several occasions. Clary had demanded that he kept himself safer, and he agreed, only when she said she would keep seeing him in secret.

But that secret had become too much for Clary, and the night before her wedding to another man, she cut him off. "I can't keep on doing this Jace!" she had cried. "This thing we have is so wrong that I can't help but think what would happen to us if anyone knew."

That had been when he suggested running away, and she hastily agreed, at the time. Looking back at the previous night, Jace could see that she had possibly only agreed to keep his anger at bay. She never really meant it.

He laughed then, at the absurdity of the situation. Valentine, their father had really had the last laugh before his death. Jocelyn, their mother, was relieved to know Jace was alive, but she kept her distance—he had been her demon child after all. She never loved him.

But he loved Clary.

The wedding was to be held in an old library, just outside of the city. The guests were limited, only sixty or so invited, but Jace felt alone the whole time. Isabelle held onto his hand in a very sisterly gesture, the type Clary should have been able to do, but would never be able to accomplish without his heart rate stepping it up several notches. They sat somewhere in the middle of the rows, people Clary knew surrounding them.

Jace made a quick note of his attire; a white dress shirt and dark brown pants, in contrast to Isabelle's bright blue dress. He felt like he was attending a funeral.

Everyone stood up as the wedding march flooded the small room. Jace waited, watched, and then finally, Clary was there. Being walked down the aisle by Luke, she glowed. She wore the simplest of dresses, framing her perfect figure flawlessly. Jace could feel Isabelle squeeze his hand tightly, keeping him grounded. He let himself imagine she was walking toward him for a quick moment, only until she walked past him, but not before she sent him a fleeting look of astonishment. Obviously she thought he wouldn't show.

He didn't take in the rest of the details of the ceremony, letting it roll past him like a bad dream, until the two words were spoken from Clary that he never thought he'd have to hear for someone other than himself.

"I do," she said so quietly, Jace almost didn't hear it at all. Clary's eyes flashed to Jace's so fast that he wondered if anyone else caught her glance.

He had to look away when she kissed her new—mundane—husband. She had turned her back on the Clave, not wanting any part of their world. Marrying a mundane was allowed.

It was done, and the new couple walked down the aisle together, their audience cheering loudly for them. His nightmare couldn't have been worse.

If only, he thought mournfully, she was mine.