A/N: This was initally supposed to be a House fanfiction, but quite quickly morphed into a Callian piece. I think I was desperate for a reason Cal had been such an asshole in season 3. This is one of the reasons I came up with and it's really more a character study than anything else. I hope you enjoy!

Happy. He remembers the feeling, tastes the remnants of it on his tongue. It used to come easily. It used to be natural. Now, it only comes when he forces himself to feel it, plasters a smile onto his face and pretends it's there until he almost believes the feeling's real. But it isn't. It never is. He often doubts it ever will be. So for now, the pretense is enough. He can't have it any other way.

If he lets the truth come out, if he lets himself admit that the happiness he wants so desperately evades him, he will have to face the ugly, jarring truth of his feelings. He is jagged edges and sharp corners. He is shards of glass. He hurts everyone who dares touch him because he is so broken in and of himself.

And so he builds up a wall brick by brick to keep everyone out, to keep her out. He never wanted to hurt her, he really didn't. But he did. And that in turn, hurt him. But what he didn't expect was that encountering his carefully crafted walls would hurt her more than any of the wounds he had ever inflicted upon her. He seemed to have forgotten that if anyone knew true pain, true brokenness, it would be her. He had watched as she was torn apart by despair time after time, heard about even more instances; the pain her alcoholic father and absentee mother caused, her addict ex-husband, the woman who had given her the child she wanted more than anything in the world only to tear her away after only 57 days, the man who killed one of her closest friends. They all hurt her, nearly destroyed her. He was almost surprised that she could manage to pick up the pieces.

And still, she was such a bright spirit. She experienced a nearly juvenile sense of happiness at the smallest of things, like chocolate pudding and wedding ceremonies. She found joy in them, genuine joy which crinkled the skin around sparkling blue eyes and revealed her straight white teeth and the pink of her gums. And it was beautiful.

It was when he saw that smile, that smile that made his gut clench with longing, that he wanted to protect her from everything and anything that could hurt her, including himself.

He could never be enough for her, never. He couldn't be better than some of the people that have passed through her life. He could never be better than Dave Burns or Atherton or Gianelli, his name didn't matter because he was bloody Captain America and all he was was Cal.

He loved her, he did. But he was terrified of contaminating her, of making that smile she wore so brightly twist and droop into an expression of pain, mirroring his internal one. He didn't want her to allow the hurt she'd experienced become a centralised aspect of her sense of self. He didn't want her to become like him.

But she had already begun to; he noticed every change. She began to call men 'limey bastards' and say 'oy'. She stopped grimacing when he'd continually offered her beans on toast and actually ate it, almost seemed to begin to like it. Parts of him were becoming engrained in her. And while that made him feel so full of pride and love, it also devastated him.

If he loved her, truly loved her, then he couldn't have her. He had to allow her to find a man who could give her the things he couldn't, who wouldn't put that exasperated expression on her face every damn day because he couldn't help but be frustrating, impossible.

If he was completely honest with himself, he just knew she could happy for years just being the type of best friends that were so close, so in-sync, they were often mistaken for a couple. He didn't have to risk shattering her once and for all if he never pushed for more. He didn't have to hurt her, he couldn't. She was too good, much too good.

He sometimes wished that things were different, that he hadn't fallen in love with her while she was in love with someone else, that they didn't work together, that they didn't need each other, that they didn't have so much to fear losing. But he knew that in the absence of those things, his love for her wouldn't be so strong, so consuming. It was choking him. His love for her was suffocating him.

He tried to pretend it wasn't there by burying himself in meaningless relationships with a horde of other women, but not a single one could erase her from his mind because she was utterly irreplaceable. That realisation only intensified his fear of losing her.

If he lost her, he would lose everything. Everything. So of course, he couldn't fucking have her. Not even when he realised that she wanted him. Him.

He could remember so clearly having seen it in her eyes. He hadn't even done anything special. They were just talking about a case they were working on, trying to understand why the husband was lying and she took a moment to look at him, really see him. And before steeling her features to his returning gaze, he saw it. Not only the fog of lust, but affection and happiness. It was an almost-love there on her face just for him.

What he wanted was to explore every one of those emotions, show her that he returned her sentiments. But he never could. Because if he let the truth came out, he could lose the only person (apart from Emily) that he couldn't live without. And he couldn't do that.

So he pushed her, played on her weaknesses, weakened her strengths. He tried so damn hard to make her loyalty falter, make her hurt so much that she would stop loving him. But his worst fear came to light when he saw it through her (very real) show of sorrow. He was already too late.

She could not stop loving him.

There was no way to mend that. And now, he felt there was no way to mend the relationship he'd destroyed. But he'd have to try. Because there was no way, no bloody way he'd allow himself to lose her now.