Sometimes, the Doctor remembers.
It's a whisper in the corner of his mind, his conscience. It's the teardrop in the corner of his eyes whenever he sees a school. It's the sudden wave of grief that overcomes him in the middle of nowhere.
He's reconstructed his times with her through the holes she left behind, but it's not the same. He doesn't know what she looked like. He doesn't know where she was from, or the sound of her voice. He doesn't know the small things, the big things—the things that are to be remembered.
One day, he ends up in Victorian London. He doesn't know what led him here, and it feels like he's missing something. But he shakes it off and decides to go see a play.
He takes back roads to the theater, through quaint roads and by mansions. Outside of one, he sees two children playing with someone who is presumably their nanny. (Children, he thinks. Something about children and Clara.) They're giggling, laughing, and it evokes a sort of nostalgia deep within his bones—
A school, a classroom. A woman writing something on the board as twenty-five teenagers look on, seemingly enraptured by the sharp twang of her voice. He can't quite place it, but it feels like home.
And he knows he's missing it, that there's something so important about this memory, but in a split second, it's gone, and he's left with nothing at all.
The children and their nanny wave at him as he walks past them, and he waves back.
He doesn't know why.
He's haunted by ghosts.
All the people he's left behind, all the people who have left him, all the people who have left the world. They wait by his side when he goes to sleep, follow him around every waking moment. He knows they're not real, but every so often, they get the better of him anyways.
Sometimes, it's Susan, wide-eyed curiosity and brown hair and laughs just out of his reach.
Other times, it's River, blonde curls and sarcasm and two hearts, beating in unison with his own.
It's Barbara, Ian, Jamie, Sarah Jane, Romana, Ace, Rose, Martha, Donna, Amy. It's everyone he's ever lost, everyone he's ever hurt, everyone he's ever failed.
(Failed them all, he has. They all deserved so much better.)
And sometimes, he can't quite tell who the ghost is.
All he knows is that it (she? something tugs at his memory, but he can't figure out what it is) has been with him for a long, long time.
The Doctor doesn't deal with loss. That, perhaps, is antithetical for him.
But he remembers.
And he hopes that someday, he'll be able to make it up to everyone he has lost.