This Hentai is odd in that the sex scenes provided character growth for the male protagonist. The female protagonist is also not the initial love interest. We see these two protagonists offering each offering something during their time together. Although the female protagonist does enjoy sex which is provided by the male protagonist, there is also the notion that she is actually a kind lover and teacher beyond her role as part of the school faculty. She coaches him in sex and he gains confidence through their numerous liaisons. One might also argue that they could also potentially become a couple, but the end doessuggest that he might have made the decision to be with his love interest. Is the female protagonist likely to rely on their interactions to be happy? No, but there did appear to be chemistry there in spite of the age difference and power dynamic.
To the question of whether or not the male protagonist is cheating... I would argue that this is up in the air given that his relationship was effectively put on hold during his time with the teacher. We basically do not see the pair interact at all during this time, even though his love interest is pining and worrying about him. That suggests that he has taken time off to work on himself.
All in all, this is one of the most tastefully done Hentai that I have ever seen. Given the focus, it seemed more of an explicit coming of age story about a young man's sexuality. This made it more enjoyable for me personally, and something that seems to have annoyed a few viewers that have posted feedback in the forums and on some other websites.