In Gravitation volume 2, Yuki and Shuichi have a rather risque encounter where Yuki borderline-forces sex on Shuichi. (No worries— he doesn't actually. When they do it 20 or so pages later it's completely consensual.) Anyway, this distresses Shuichi a lot but is pretty much laughed off, so to speak, by the end of the volume. I recently realized that this incident was not just Yuki being a bastard or having a huge sex drive...he is acting this way because it's the only thing he knows how to do. Yuki's only experience of love so far has been his hated family, overprotective Tohma, constant casual sex with any slut who knew his name, and the horrifying Kitazawa incident. That is, his only perception of love is a) an annoying, troublesome and obligatory thing (familial), b) something that means absolutely nothing (sexual), and c) something horrible and painful that will only hurt you and must be avoided at all costs (emotional). If you know his backstory, who can blame him? So Yuki is not just being a jerk...he's genuinely confused when his coping mechanism doesn't work on Shuichi. That just makes their whole situation that much more heartbreaking.