It's the humanity in the Doctor, which Martha and all the Companions have forged and will continue to forge, that keep him on the path. Life is balance and it's a constant working: Grace is a wave that never breaks.
Tallulah's song for Diagoras plays in an alien cantina, where many races from the last five years can be found. Jack Harkness sits at the bar, a thousand miles from Gwen and all that death, and the bartender brings him a note from the Doctor. He looks up, shocked, and locks eyes with him: The Doctor salutes. He knows now what it's like: To be hard, to be soft. To be a man. He has forgiven Jack for that, and so much more. His name is Alonso, the note reads, and the Doctor gestures to Jack's left, just as Midshipman Frame sits down, still in his Titanic uniform. Allons-y.
Stories end, and you don't. In those tiny moments of grace to which you tend, if you have the grace to accept them, at those rare times in the angle of the light where the words reach out and lift you up, you are touching something bigger than anything that could ever harm or stop you. You are the Bad Wolf.
Pretty Verity explains to a Pegg knockoff about her great-grandmother, Joan Redfern. She bears a startling resemblance, of course. "She was a nurse in 1913, and she fell in love with this man called John Smith. Except he was a visitor... From another world. She fell in love with a man from the stars. And she wrote it all down." She slides the book across the table -- The Journal Of Impossible Things -- and thanks him for buying it. The next man asks her to sign it for "The Doctor." She smiles, until she meets his eyes. She takes him in.
"Was she happy? In the end?"
Verity smiles. Of course she was. She was wonderful.
He smiles. She watches him go.
Somewhere in space and time there's a singular entity whose Companions and collections and victories comprise a history, an infinity of windows into time. Whose halls and memories and fears have been walked by a select few.
Bells at a church, after the wedding's ended: It's the Temple-Nobles! She screams a lot, abusing Nerys -- "You made me wear peach." That's because you are a peach. Furry skin, stone inside, going off -- and shoving everybody around to get their pictures taken while Sylvia and Wilf look on, leading the cheers and weeping for joy. Minnie goes after Wilf one more time, as Sylvia sees the Doctor, just beyond the garden.