You can avoid all forms of other people having sex with other characters minus the hooker that is used to seduce the guards for a mission. But lets be real thats not ntr, and the threesome with the giant and the priestess but you're not really in a romantic thing to begin with I mean she worships a sex goddess doubt she's gonna settle for one guy. The goblin is avoidable by simply not accepting/doing her final wedding quest and thats it. Everything else you can skip through and miss out in a lot of scenes which ain't worth it lets be honest seeing a giant ram a thick bimbo is fun to watch.I only started playing this game since the tags had "NTR (Avoidable)"
Wasted my damn time if that's a lie