He wanted to sit up, to show her how serious he was, but he also didn't really want to move. Instead, Rabastan just looks down to meet her eyes as best as he can.

"Absolutely! I mean that, any time!" he said, maybe a bit dramatically. He wasn't the best at wooing a woman, and he hadn't quite figured out that complete and utter--to the point of obsessive--devotion wasn't really what most girls were seeking in a long-term mate. So it was his default plan, most of the time.