Wow, it's all coming full circle, originally the girls who seemed like they should have some self-respect acted like they had none, and Kotonoa, who seemed like she shouldn't, got more and more. Now, after Itou has fucked pretty much every named character except the tall lesbian-looking girl (who only aims for teachers apparently) the girls have finally managed to find some self-respect, or in the case of Katsura, realize that they really have none and are completely defined by the people around them.
I would agree that Itou doesn't deserve anyone, but it's clear that Kotonoha is completely lost and is lacks the mentally fortitude to not be with Itou. So for her sake she has to be with him. I don't think she actually cares about what he does on the side as long as he's with her some of the time, and with any luck he'll either a) have such a bad rep that no other girl will talk to him or b) have actually learned something from being left high and dry by his harem but stuck with by a crazy Kotonoha and he'll treat her right......*pause for lols*
@animus: I suspect that the more random sex scenes (Kuroda's girl and the Trio) is just leftovers from the anime makers trying poorly to fit as many different scenarios from the game into the anime at the same time.