"Oh, Martha. It's not wrong at all." The Doctor gave her a sympathetic smile. "I don't know precisely how any of this is going to work out in the end. The fact that none of us seem to remember being sidetracked to this time and place suggests that either we won't remember at all, or history is being rewritten. I can't say what will or won't stick when this is all over. Just at the moment, I'm inclined to tell you whatever you want to know."
After all, if history was being rewritten, then what came next didn't particularly matter, did it? It would never happen. Somehow, the Doctor didn't feel that was the case. If it were, he would have felt the effects. Worst case scenario, he would have begun fading from time, because he would have walked a different road with a different Martha.
"So. What is it that you want to know? I won't promise that I'll have answers for you, but I'll try." He owed her that much, didn't he? It would be cruel, to lead her on now that he was consciously aware of her attraction to him.