Regarding the NTR: It's definitely more of the last two. If you lose fights, the girls can get raped. If this happens multiple times, the dialogue can change where the girl starts to enjoy the sex. There is also a netorase part where the MC can "develop" a NTR fetish, which will be reflected in dialogue when he's peeking on girls with other guys. You can also corrupt the girls, which will cause the dialogue to change where the girls start to fantasize about sex with others or become very open to sex. However, ultimately, the girls all still love the MC. I don't think there is any situation where the girl outright hates you or is indifferent (there is at least one girl who you can close out the romance route with but you need to have not had a relationship with her prior).
Regarding the second part: IMO, this is a chad MC kind of game. The MC is this warrior who goes around and does a bunch of crazy shit. He saves a village, he slays monsters, he defeats demons. The role of a weakling cuck doesn't really fit him. If you want to twist the narrative a bit, you can say the NTR happens from a lot of reasons: "he neglects his girlfriend", "he started off weak and because of that he lost his girl", "the girl is just always a slut". It's never really a "small dick MC" or "bad at sex" kind of thing since all the girls eventually come back to him.
