Just finished my first playthrough of the game, and tried to pick every (
major) NTR option available, but it still seems like it ends with you two on the NTS path for now (
she shows Ben her tits despite your protests, but apologizes and you two agree that it was hot).
It would seem you have to avoid keeping up the Love stat too high via the numerous (
minor) choices (
like, avoid responding with "Love you, too") to get on the true NTR path, but that just seems like you're acting like an asshole to your gf, which takes away (
to me) one
important aspect of NTR - that it doesn't have to be a
direct consequence of your actions, but rather the sum of a series of unfortunate events, somewhat influenced by your actions.
If I have to act like an asshole that barely shows affection to his gf, then it's no wonder she would cheat on me - but if I do a good job of being a good bf, and shit still goes wrong because something I couldn't necessarily control, that makes the cheating even better, IMHO.
Hopefully, I am wrong, and you don't have to be an asshole to get cheated on here,
UnzippedGames