NTR is unavoidable(story mode) unless they changed something from when I played(ver. 1.22?).
I don't think your character can initiate any kind of sex act with any character, maybe at the end? I'm pretty sure you can get married to a custom character so I would suggest not getting too attached to the heroine(until they add a route where you can avoid NTR).
I did pretty much quit playing after that point so I'm not quite sure what else can happen and I don't want to spoil too much for those that'll enjoy it.
I did have fun with what I played but there were times where I used cheat engine to speed things up(it will bork your game and crash so I wouldn't rely on that too much)