Sorry but that definition is simply wrong. Not trying to beat up on ya as it's a very common misconception I see on F95.
NTR originally stands for 'netorare' which is japanese speak for cuckoldry. Basically when a character's love interest (or LI) is 'stolen' by another person. That type of activity is not present at all in this game (as far as I'm aware and I've pretty much played the entirety of this game until this latest update).
However, people on F95, apparently you included, often cross it/confuse it with two other similar words. 'Netori' which is when the MC is 'stealing' another person's love interest (lots of that in this game) and 'netorase', which is essentially swinging or sharing LI with someone else. Netorase sort of happens in this game but its a bit of a stretch to say that. My opinion, it's hard to truly nail down what netorase is since, in essence, a threesome could be considered netorase. Like when the MC is sharing the mom with the motel manager.