@emMeBi86: Haha, you're totally right. He might as well have summarized it as: "I don't want to be with you because my influence is making you too horny." What guy in his right mind would do something like that, lol. But wait, did he actually have sex with sensei? I don't recall that exactly happening. This whole chapter felt like the author monologuing exposition for why Keita is the way he is lately to us his readers. Personally, I'm happy for Mikuni; now, she can find someone who isn't a shallow douchebag. I really hope though that she doesn't continue to linger around, like sensei, having not actually moved on, despite saying so.
I have to say, that at this point, the author should wrap things up. I can only guess that Keita will end up with none of the current girls in particular; honestly, for the sake of his own well being, he should just get to know some other random girl , someone who's completely apart from the total clusterfuck that his life has become.