The Doctor knew, once, that humanity wasn't his plaything; that Earth was not a playground but a new Eden, that held him to her bosom. How did he forget? Where did that knowledge go?
("The man who abhors violence, never carrying a gun. But this is the truth, Doctor. You take ordinary people and you fashion them into weapons. Behold your Children of Time, transformed into murderers. I made the Daleks, Doctor. You made this... How many have died in your name?" Jabe, Controller, Lynda, Sir Robert, Mrs. Moore, Mr. Skinner, Ursula, Bridget, Face of Boe, ChanTho, Astrid, Luke Rattigan, Jenny, River Song, the Hostess. "The Doctor. The man who keeps running, never looking back because he dares not, out of shame... I have shown you yourself.")
And then his family deserted him, scattered to the winds. And his sister, the human Time Lord that could have travelled with him forever, could have kept him human, never running away again: He took her into his arms and he killed her. At her door, Adelaide turns to look back at him: Heading back to the TARDIS, victorious. Above all that chaos and death. Not the last, but the first of something new and terrible. She takes out a flash gun as the bass comes up (the day Rose died, on Bad Wolf Bay; the day he took Doctor-Donna in his arms, and killed her while she wept), and closes the door softly behind her, and she pulls the trigger.
And at the TARDIS door, he whirls in the light of its pulse, and time rights itself. Like water. Adelaide Brooke died 2059, no matter what. History changes around him, and he shivers, gritting his teeth. Time Lord Victorious was wrong. He is paralyzed, suddenly realizing what he has done. The perversity, the pride, the selfishness. The hatefulness of a Lonely God.
The Doctor learns shame. There was someone to stop him, someone to save him, after all.
And on the corner, in the snow, he can see Ood Sigma, watching; he drops to his knees. "I've gone too far. Is this it? My death? Is it time?" Sigma only stares a moment before disappearing, and he finally stands, shaky. The Doctor opens the TARDIS and steps inside, looking around guiltily before he closes the door, swearing something. That he won't die, that he will survive this, that he won't touch time again so roughly. The robot stands in the street, in the snow. Alone. The Doctor stares past her coral works, neither up nor down, and sets his course. All he wanted was for her to love him. The Cloister Bell is ringing.