"Can you change back?" she asks, her eyes so full of hope.
He'd seen that kind of hope before. In someone else's eyes.
Someone else he now remembers with painful accuracy, right down to the last heavily mascara'd eyebrow above her eye. Someone he hoped he never would have forgotten, and yet the proof that he has is standing right in front of him.
And now he knows why he fell for Joan. Why this woman, despite being so wiser, reminds him of someone else so far away.
But they're different, whispers voices in his head. One lost a husband, one lost a father. One is younger, full of imagination and the other is older, wiser, and knows better than to believe in silly things like aliens and monsters.
"Yes." He says, as simply and succinctly as he said it the last time he heard those words.
"Will you?" she asks, edging closer, as if she's straining to hear his voice.
By all accounts, yes, he can. He can live a life, have children, grow old, just like he saw from that little watch. Those few visions that made it that much harder to let go. To turn back. To say goodbye. To die.
But by similar accounts, he can't. He can't turn his back on the universe, he can't let things happen they way they would without him. He can't let people die, he can't let time get disrupted from her course. He can't leave the TARDIS behind.
But in the end, he does have it. He has a choice. Yes or no. Human or Time Lord. Old age or immortality.
The difference between Joan and Rose is rather clearer now.
He fixes her with an even look as he gives his answer. "No."
And that's the truth. And that's the difference.
He knows, that if he could have changed back to his old self when she'd asked all that time ago, he would have.
He knows that if Joan had been a different person asking him the same thing, he would have said yes. He knows that if he had been someone else, he would have said yes, but he's not. He's the Doctor. John Smith, no matter how many times he tells her otherwise, is gone.
He asks Joan to come with him, even offering her a chance for them to be together. At least a shot. Which is more than what he had given anyone, even Rose.
But he hadn't been human then. He had fallen in love, oh yes, but he had never pursued it. He would never have allowed himself to. There were so many futures and so many of them ended in heartbreak. And he didn't want to face that.
This whole adventure makes him wonder all the more at what would have happened if he hadn't been a coward. If he had been willing to risk losing the one he loved so dearly if it meant that they were together. If he had been willing to watch her die if it meant he had more time with her.
But that's it, he supposes. Differences and choices make people who they are. John Smith and the Doctor, no matter how much they are alike, how much they look alike, are not the same person.
Both of them gave their hearts to humans, both of them lost their hearts to humans, but one was willing to have loved and lost than have never loved at all.
John Smith wasn't lonely. John Smith had a life. John Smith had a love and a predictable future. John Smith had one heart and a human brain.
John Smith, in the end, was a much more courageous man than the Doctor ever could have been. John Smith would have allowed himself to love, whether he saw a future of heartbreak or not. Because John Smith would have known, that not allowing himself to fall in love would have hurt more in the end.
