There's maybe three or four instances of what I guess could be called "NTR" in this game and they're all avoidable/optional afaik:
- Riley will try to make the main character jealous by attempting to seduce some random guy if he hooks up with the girl on the plane (iirc she only kisses him, and it doesn't happen at all if you don't cheat on her first)
- The mom and the older sister are revealed to have been having an affair with each other for months, hiding their relationship from the rest of the family. The main character can find out about it (it's optional, but the story will still have some hints about their relationship in the dialogue) and there are some scenes where he spies on them together. At one point they can have a threesome with an old (female) friend of the mom's. Tbh, I don't even know if this counts because a lot of people only really consider M/F stuff to be "NTR", but whatever.
- There's one scene early on in part 2 where Riley's mom is giving Riley's dad a handjob while the younger sister watches them. Riley's mom is teasing her and, iirc, trying to seduce her, but she leaves before anything happens. The MC can either spy on them or could completely miss this event, in which case it doesn't get brought up at all (iirc).
- The MC can spy on the mom and the dad having sex in a few instances (listening in on them in the bedroom in part 1 and spying on them from a far in part 2). Both scenes are completely optional. I don't really know if this counts as "NTR" either (if anything, the mom eventually having sex with the MC is netori, lol).
The mom wasn't the one under the desk, if that's the scene you're asking about, no. It was some random girl that the MC and Riley later meet while leaving on the plane. She propositions the main character in this one encounter and then completely disappears from the story, iirc.
