I think that's a chapter we're supposed to have difficulty grasping as westerners as 'taking responsibility' doesn't really mean anything to us, or at least it's not as much a big deal as in Japan. I think Seto's issue here is that he must have been plagued with the idea that sex and sexual impulses are impure, so having them and indulging on them would mean his love for Anjou isn't.
This is obviously dogshit but we can see that confusion plaguing him again at the end. He obviously wants to kiss his girlfriend but some voice in his mind tells him it's 'wrong' when it's perfectly natural.
Boys and men unable to see girls and women without the suffocating prism of the madonna/maiden vs whore image is a disease that I would hope we'd be rid of by now but it's pervasive.
Taking responsibility would mean realizing once they do the deed that it doesn't change anything about how he views Anjou, who was simply a human with needs just like him all along, not some ideal to corrupt. Because I would guess guys that do not take responsibility are ones that have this switch flip once they bone a gal, which is so stupid and such a virgin way to think.
Having sex with someone once usually sucks! The good stuff comes right around the third time when you start to know what each other like!
