One of the girl get raped(by a teacher), she quite enjoy it, but in the end, they don't like being blackmail, so they report the rapist, then all three of them got transfer into the main school, they interact less and less, until the end they all goes their separate way.
The sex are mostly either threesome or the guy with one of the girl. The girl does do yuri stuff during the threesome, it mostly about sex, so it pretty casual about it, no one really become lover. So after being transfer, they all join different group, and goes their separate way, which is kind of sad, since It feel like they starting to develop a relationship a bit before chapter 30.
I don't consider it NTR, since it rape, but they do compare the guy with the teacher, so kind of semi ntr there(even though they are not lover, and there is no feeling of betray)