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Looking into Joan's eyes, the Doctor knew there was nothing he could say to change her opinion of him. He wanted her to join him, he really did, but never the way John Smith did, and she knew it just as well as he did. John Smith could really love her. He couldn't.

"Would anyone here have died?" She asked, and he knew there was no good answer for that. If he hadn't arrived to this village, to this school, if the TARDIS hasn't sent him there, no one would have died. Not at this time, in this place. What could he possibly say about the lives saved in the future, when she was a human who never traveled amongst the stars? The people she worked with and lived with had died, and that was all that mattered. And in truth, he, too, felt that saving a few in the future isn't worth a few dead now.

So he left. He walked away, his coat moving on its own in the cold November breeze. He walked across the fields of England, his hands in his pockets, and thought of all he could tell her, if only the time and place were right, if only everyone were still alive. He could have told her that she was wrong about him; wrong about John Smith and his relation to the Time Lord called The Doctor. He could have told her that she and John were wrong about the reason he didn't mentioned falling in love when he briefed Martha. He could have told her that he's more scarred than she could ever imagine, after losing countless people he loved.

But there was no point, and he knew it.

As he flew the TARDIS away from 1913 England, his mind returned to Joan and love. He remembered Martha telling him she loved him and knew it was real, even though he pretended it wasn't. He remembered falling in love with Joan; kissing her; dancing with her; but it was all from another life. When he thought of love, the only face to come up in his mind was a young, blonde woman's face. Rose Tyler, his mind echoed, even as he talked to Joan and Martha. My Rose Tyler.

Oh, that was love. Yes, the Doctor never even thought about mentioning falling in love, but not because it was impossible for him; because a Time Lord's love, just like his life, lasts forever. He loved his wife more than anything, for hundreds of years, even after she died in that bloody war. If he could, he'd have given up his life to save her. He'd have given up his entire future, even saving the time-space continuum, just to save her. But he had to watch her die, and for an entire century he could find no way to cope but run away from one place to another, escaping the memories of his family burning as they tried to protect Gallifrey. Until he met Rose.

He loved her. He knew it from the very first moment he saw her. After the burning of Gallifrey, he decided to never take anyone with him again, to never get attached to anyone again. He didn't mind if it was a human or a robot or any other thing. All he knew was that after so many years of losing people he loved, he's had enough. But that was all until he met Rose. Because when he met her, when they ran towards the London Eye, when she saved his life and her world, he knew that he had to have her by his side. He had to have her traveling with him. He had to never let her go.

He burnt up a star just to say goodbye, but he wanted to do so much more than that. He wanted to burn up the entire universe just to bring her back. He would have, if he wouldn't have gotten involved in something else in that moment. He would have burnt Gallifrey all over again if he could just tell her he loves her and will find a way back to her. If only that were possible.

And that... that was why he could never love Joan the way John Smith did. Because the Doctor could never stop loving someone just like that. Humans fell in love quickly, and he forgot it, simply because he couldn't imagine falling in love like that, not in the next few centuries at least. His heart still belonged to Rose Tyler, and there was nothing anyone could ever do to change that. She was the only reason he kept on fighting like this. She was the only reason he kept fighting for humans. She was still his love, and he couldn't imagine loving any other woman.

But how could he explain that to Joan, who thought he'd approved fighting and murder? How could he tell that to "John Smith", who knew nothing of the burden the Doctor carried and the things he'd faced?