That stung, the insinuation that he didn't know what love was, that he was incapable of falling in love, that he had no idea how much it might hurt to walk away. The Doctor's expression turned dark, and he felt his temper threatening to take over the conversation. He held the full force of it back with an effort.
"Didn't you pay attention to what you were writing in that journal of yours? Didn't all that time you spent dreaming of a woman with blonde hair give you any hints? Maybe it didn't occur to me that you might fall in love because there was already someone else. I know how it feels to be in love and then lose everything overnight. That woman in your dreams is real. Her name is Rose Tyler, and I lost her. I lost her until the walls between universes began to collapse and she slipped through the cracks to find me. I've died for her, and I would do it again, so don't you dare tell me that I don't know about love."