Falling into some sort of routine where they chatted before bed felt--well, it felt the same. It was comforting. When it had been just the two of them in the TARDIS, that was how things were. They'd chat until there was nothing more to say or an adventure popped up out of the blue. Granted it hadn't been quite like this, the Doctor liked the shift. He looked forward to it at the end of his awfully linear days as a sort of hideaway from the natural progression of time.
Hearing her speak then, he turned back onto his side to watch her. Giving her his undivided attention (well, as best he could), he listened closely. He could hear the hitch coming and braced himself for it, though the Doctor didn't completely understand why. Relationships were a tad foreign to him, at least conventionally speaking. He'd been with people before, but Rose was unquestionably different.
And she was jealous of River.
If it had been this face to marry her, he might have understood it. For the moment, the Doctor appeared terribly lost. "Jealous? Of River? Why? She'll be his wife, not mine. Nothing to do with me."
All of time and space tucked under his belt, and the Doctor would never fully comprehend the human perspective.