So far the NTR or at least NTR-ish stuff is not avoidable. To be clear though, there is no sex (so far) between the girls the main character is interested in and any other guy than the main character. However, there are cases of some of the girls going out on dates with the main character's rival, and they do end up in bed with that rival, although according to the devs there was no actual sex and won't be. But a lot of people are uncomfortable with stuff that has happened thus far, because that's basically what the devs were going for.
tl;dr: The content isn't avoidable, although it's not "hard" NTR so far where there's actual sex with a guy other than the main character. If you're the jealous type though, the game tries very hard to make you feel that way.