Disclaimer: I don't own Doctor Who.
He gets bumps and scratches a lot. He can't help himself. It's the way he is.
She wishes he could though. He's not invincible, she reminds him every time she has to patch him up.
*****
The first time it happens, it's a girl not looking where she's going. Right out into the street, with a van coming head on.
He can't help himself. It's in his nature. He runs out and pushes the girl out of the way. The van clips him on its way by.
She's crying when she tells him that he's not invincible this time. She's crying and she wants him to promise that he won't ever do something like that again.
He tries to, because she's crying, but his words are slurred by the pain meds.
*****
He can't help himself because it's in his nature. So it happens again and again, until he's made her cry so many times. And he tries to stop himself because it makes her cry, but then a part of his mind wonders why she's crying if he saved someone. So he doesn't stop.
It's when she decides that he needs help that it becomes a little surreal. She gets him a therapist, and tells him to talk to the therapist. So he does. He tells the therapist about all of time and space, and how being stuck here made him realize what all of his companions went through. How they all felt like ants who could do nothing of importance. How he's trying to do something of importance, one person at a time.
The therapist decides that he's crazy. The therapist is fired, and the idea isn't mentioned again.
*****
And it happens again and again. This time a new therapist is hired, one from Torchwood, one who would, if not believe, then go along with the stories of time and space. So he tells the therapist stories about time and space. How, stuck on this rock, he misses it. He misses the adventure and the running, and the being someone. Sure, he never stayed around for thanks, but he still knew that they thanked him, and spoke of him in reverence.
The therapist decides that he's having problems adjusting to life on Earth. That, and a side of crazy. The therapist is fired, and he notices her smile crack a little.
*****
His body is falling apart. He's noticing it, day by day. He's lost track of how old he really is, but this human body is in its forties now. Aren't they supposed to last longer than that?
He places that query to her. Her smile, already cracked, cracks a little more. He thinks he sees her shatter, but he can't tell.
His joints are stiff now. Some days he can barely walk without limping. And his hair, his beautiful hair, is starting to lose its color.
He understands what she's been saying now. He's not invincible. And he's never had to deal with long term consequences like this before. Time Lords healed so well, and he had never quite managed to switch that mentality off.
But that new knowledge can't stop what's in his nature. And if he goes about his nature a little slower and more painfully than before, so be it.
*****
She's crying again. She's warned him so many times. But he couldn't stop. He just couldn't. She could see him trying, but he always gave up in the end. She'd never seen him give up like that before. He'd blown up a sun to say goodbye. Why couldn't he stop himself from doing this?
She loved him. And now he's gone. He saved her, and now he's gone. All of those people saved before, and all she could see was his slowly rotting body.
And now it's her he's saved. And she wishes he hadn't because now he's dead, and she doesn't know where to go from here.