To make a long story short, NTR is about the feelings you get from things like Cheating. Female led NTR is about the corruption, while male led NTR is about feeling bad in an erotic way. Netori is about the feelings of superiority from stealing someone away and such. This is why it's not explicitly cheating, since you can have those emotions even without cheating, like a pretty good NTR manga had the MC just be a loser who found out his crush was dating the guy he didn't like. Tell the truth IDK anyone who felt bad for the MC of that one.