Nine centuries of traveling through time and space, falling into and out of mischief, cleaning up the galaxy's messes and occasionally creating a few of his own. And then the War came. The one thing that was too big to avoid, or talk his way out of, or fix. The thing that forced him to commit an act of such total destruction that it would silence two races for all eternity. The guilt in his soul and the silence in his head drove him to the brink of madness. He grew reckless in his adventures. There were no companions to look after now. He was all alone, and rightly so, so what did it matter if he blew himself up in the course of saving the day one last time? It was no more than he deserved.
And then he met her. A nineteen year old shop girl from Earth, who was currently curled up asleep on the jump seat, wrapped in his leather jacket. She led him out of the self imposed exile of his own mind, showing him that there was still light and laughter and love in the universe. Even if he was too damaged for love, it was nice to see that it still existed. He wonders how long the universe will allow him to keep her. He wishes it could be for always.
He gazes at her sleeping face with unguarded affection, then stoops to gently brush back a lock of golden hair and drop the ghost of a kiss on her forehead.
His face changes, becoming younger and more conventionally handsome. His manner changes as well, smiles, and laughter, and hugs becoming easy and frequent. She allows herself some fantasies of always and forever that feature white dresses, and flowers, and rings, and laughs at herself, knowing he will never ever stop running long enough for that…not even for her.
He tells her that she can spend the rest of her life with him. He knows it will kill something inside him to watch her age, and wither, and fade from him, but he never could refuse her anything, so he will revel in the forever that she promised him, knowing that his hearts will shatter when she is gone. The shattering comes without warning, in the form of a Dalek, and a blank white wall, and a parallel universe that he can never return to.
He is alone again, and reckless, again, but he has friends this time, and they manage to keep him anchored until she finds him once more, and he loses her…again. But at least she will get to keep a part of him for always. And him? He will go on alone, but for now, he can have one last glimpse of her, just before the start of their forever.