Who watches the watcher is a really old question, but who heals the Doctor's asked a bit less frequently.
Maybe, he thinks, as he watches the light dance over his fingers, golden glow like fireflies and stardust and orgasms made almost-tangible, there's a reason for that.
It doesn't matter.
Rose is scared, and crying, and he can't explain it to her. There isn't time to do it, and there aren't words to do it, except. Except.
You were fantastic, he says, and he means it, and it means I don't want to go and it means I love you and it means It was always, always, always worth it as he grins the grin of the oncoming storm at the girl who's companion in more ways than one.
And then the light starts to build inside, and he knows about time, knows about seconds running out and there not being many left, and knows about there only being enough time to say what matters most, and what he says is, And you know what? So was I, and then it's just a moment.
It's just eternity, and everything being reborn. It's the big bang, baby, with both the bang and the whimper, and the thing is there's also a glorious, delighted laugh in the background and the sound of bells, and the smell of chips wrapped in newspaper and the taste of salt and grease. It's every moment of all the Time Lords going out in a flash, and it's the moment where it's okay because he did what he had to do. And it's the moment where he accepts, where it stops hurting, and he grins.
You were fantastic, he says, and means it, and you know what? So was I, and the glow spreads all over him and through him, and he can see it all and it's exactly and utterly as it always had to be. As it always was. As it always will be. World without end, they say, amen, and all worlds end, but all worlds always are, too, so maybe the silly, stupid, inept humans that are barely past being apes--maybe they understand a little after all.
And for just a moment, he sees it all, and both of his hearts beat in perfect harmony, and then--
No more Doctor, and he doesn't burn out and doesn't fade away.
He fades in, and there's a brilliant smile that's almost the same and is just a tad different as he tests out new teeth, but it's still a smile, and the faintest hint of gold mist like fairy dust you need to fly is across his skin as he says, "Oh! Barcelona!" and in the background of his mind there's a fading laugh in a voice from the North.
The Doctor is in.