Some of you seriously need to read up on what ntr and voyeurism actually mean before you come and complain about it.
There is no ntr in this game.
The mc said he didn't even have a crush on anyone not even his family (yes not even Rachel who's ass he honked), everyone at the party were just friends he wasn't in a relationship with anyone, no one at the party is even shown to be a LI yet, he just wanted to get laid, read the dialogue with Lilly.
The only potential ntr (netori at that) would have been with Amy because she's the only one in a relationship, but she didn't sleep with anyone. Yes ntr means there actually needs to be a relationship involved, not just when just your eyes tell you that you like someone on first glance.
Guy living with mother and two sisters in a sex game, what are the odds incest wasn't going to happen? Did it happen kinda suddenly with Lilly, sure maybe, but they were at a sex party looking to get laid, Lilly got into the moment and wanted to have sex.
I'm not a fan of ntr, but it's sad the excuses you guys come up with to bend the definition of ntr to fit your personal interest. Not every girl you see in the games are main LI either, as much as you may want them to be it's still up to the developer to define them with the dialogue, thoughts, and actions they give to the mc.
The only thing I would agree with is putting the choice to view scenes like voyeurism because like every other kink, not everyone is into that (I don't have a problem with it but options is always a good thing).