@BCS
actually, if anything, the father is totally right.
like he asked the kid. "How do you feel?"
so far it's just the kid going along with the girl.
but the kid hasn't stopped to think about his own comfort, his own sense of privacy.
sex can be about a lot more than just physicality. emotions also come into the mix, and if you don't understand how you feel, especially at a developing age, it can mess you up. he may be 15, and even his brain is developed enough it doesn't necessarily mean that he's mature or experienced enough to understand his emotions well.
the dad is trying to plant the idea of looking into one's emotions, since if he directly lectures Suguru about it he may brush it off.