A/N: The idea came from a quote I read on TV Tropes. Someone said Steven Moffat noted that the Doctor was "an angel who wanted to be human". And thus this was born. I'm thinking about working on a Torchwood/Doctor Who crossover, too, mostly because I want Jack to meet River. But that's neither here nor there.

He walks. Not when he's running, of course, or flying in the TARDIS. But when he isn't running or flying, he walks. He prefers walking to cars or buses or trains, and he's glad that no one's ever required an explanation for it beyond the fact he doesn't carry money.

Because the truth is, he could probably get onto any form of transportation he wanted. He walked because it felt so human.

The Doctor knew he wasn't. Of course he wasn't—he was a Time Lord. He wasn't even from Earth. Not remotely human. And he wasn't sure when he'd started wishing he was. Because he was pretty sure that his first self had never wanted to be anything other than a Time Lord. Or his second, or his third. Or any of him before the war, really. Even his ninth self hadn't wanted it. He'd still felt a bit of disgust for the less developed species, still been proud of his heritage.

Maybe it had started with his last self. The loneliness, the need to fit in. Missing people. Because humans didn't miss for as long. And he'd wanted the missing to end. And the disgust, of course. The disgust of what his species had become. Not so high and mighty now, were they? Or had they ever been? Had he just tried to convince himself they were?

It didn't matter now, he supposed. All that mattered was that he did wish it. Because there was nothing quite so hopeless as knowing that no matter what happened, no matter how much he tried or how many he met, he would always end up alone.

He'd been so happy, when he knew who River was. Not just because she was special (she was) or because he loved her (he did) or because there was something he had maybe, somehow, done right. But because she wasn't going to go away, not anytime soon. She had regenerations, regenerations to spend with him throughout her long, long life, and he'd seen the end of it and knew she still had hope even after the centuries.

Until she gave them up. He'd asked her not to, he didn't want it. He honestly, maybe, a little bit, wanted to die. And it was the thought of Amy (dear, sweet Amelia, who had waited for him and would always wait for him) and River that made him push away that desire. River, who needed him more than ever. Because she wasn't River yet.

But afterwards, after he'd met Mels and seen who River used to be and loved Mels too, the hurt was back. Because they wouldn't have centuries, he wouldn't have a lifetime with her. It was all too short, and he smiles when he sees her and dies inside when she leaves because he knows that he's running out of pages in his book.

She'd promised him, when she was dying and she wasn't his River yet, that they would have so many more times. That they would run together. And he clung to that, even as he struggled to learn who she was and how to trust her, because she wasn't leaving.

He'd say it to her, too. Whenever it was his last time, whenever they ran out of spoilers and stories. Because even if her life wasn't as drawn out and lonely as his, she had chosen him to be her beacon and her dream, however ridiculous the thought and however undeserving he was. So she deserved the hope that the dream wasn't over.

And even as he clings to his last hopes of seeing River, saving River, he misses Amy. Because she may be human, he may have never entertained any thoughts of forever with his best friend, but he misses her too. Because she's a bit like him, strong and hopeful and a bit idealistic (too idealistic, how could she put her faith in him?) and he's never seen anything quite like her before and is a bit glad he hasn't, because that would make her less special and he loves how special she is. But he leaves her behind anyway, because he knows he'll lose her eventually either way, and she deserves to live out her life even if it seems short to him.

Because keeping Amy, no matter how much he wanted to, would be selfish. To her and Rory (the Ponds, they would always be the Ponds no matter how much Rory protested) it would be selfish, because she deserved more than him and his lies and their adventures, even though she could live on them now. Because it wasn't all for fun, he couldn't always save her, and he didn't want her to live a short life with him. Because if they kept going, she'd die, or Rory would die, and she'd be leaving anyway. Except now, she has a house and a husband and maybe they'll have another baby, have a family. He hopes she will.

This time, he'll be far enough away he can't screw it up.

And Rory, it would be the most selfish for Rory, because Rory and Amy love each other, and Rory doesn't love the adventure like Amy does, like he does. Rory's dream really is a house and a car and a family, and he deserves it. He doesn't deserve to lose Amy to the Doctor and his selfishness, or lose his life for it, for something he never wanted in the first place.

So he clings to his quickly slipping time with his beloved River, and misses his best friend Amy, and gives Rory the life he really wants, and wishes he was human.

He'd give anything to be human. But he can't be.

So the Doctor walks, because if he ever stopped moving—

-he doesn't want to think about that.