He didn't want to burden her, but he supposed part of their newly-established deeper connection was founded in divulgence of thoughts, even (or perhaps especially) the troublesome ones. These were thoughts he'd done his best to quiet, but which were still brimming in his head. He was nearly ashamed of them.

"Sarah Jane," he turned his head away from her reluctantly. "I've never felt such happiness before. I could hardly believe it was possible. And it worries me. I'm afraid I want something from you that I've no true right to ask for."

Quietly, "You've fallen in love with a selfish Timelord."