Summary: Set just after "The Family of Blood." Did it really never occur to the Doctor that he could fall in love with a human? Why would he leave something so important out of his instructions?
This idea has been floating around in my head since I rewatched "Human Nature"/"The Family of Blood." I couldn't stop wondering just why the Doctor left out the one warning Martha actually ended up needing, and I came up with this. Hope it satisfies.
"You knew this all along and yet you watched while Nurse Redfern and I—!"
"I didn't know how to stop you! He gave me a list of things to watch out for but that wasn't included."
"Falling in love? That didn't even occur to him?"
"No."
He was alone now. Martha was around there somewhere but... Well, he didn't blame her for not wanting to be around him right now. And frankly, he was glad to have time to just think. He didn't get that chance as much as was probably good for him.
He couldn't stop thinking about what Martha had said. Out of everything, that one word. She was right; it hadn't occurred to him. Martha seemed to think it was because he was some kind of emotionless machine. In reality, it simply hadn't crossed his mind. He'd been too busy trying to sort everything else out to think about silly human emotions. Sometimes he thought his human companions tended to forget how alien he was.
Or maybe she thought he couldn't imagine an almighty Time Lord falling in love with a lowly human. Ha.
It was so simple. How could he possibly have foreseen that he would forget her? He had assumed even human, his heart would still belong to her. A heart so full of Rose there was no room for anyone else.
Maybe if he hadn't been so thick, warned Martha not to let him get attached...
People still would have died. John Smith had never been meant to last. But at least he wouldn't have left a ragged hole behind him when he went.