Responses
Well, firstly, he disguised himself as the kid who was obsessed with him to rape him so he didn't even know it was the senpai he liked until he caught him red-handed. Secondly, he WAS raped and traumatized beyond repair as you tell from his heightened desire for sex and stockholm syndrome esque behaviour. Thirdly, the guy rape many other men AND women who resembled him afterwards so...
Isn't his rapist the senpai he loved so much? If the same sensei was obsessed with him enough to rape him. Why didn't they just end up together?