I think the changing room scene was supposed to show that both girls would choose the MC. Loved that scene! Totally want to marry Anya. That girl is marriage material...in Alabama. WTF! I can move!
I get that everyone has their "thing", that rules were made to be broken, and that everyone is different. But if I had a wife/gf and she licked some guys balls without my express consent and knowledge, fluids or not, that is cheating. She might as well go all the way and get pregnant, never to return home again. But again, that is me.
Now make it into a game. There are certain conventions that we use to avoid making a game last forever without any advancement or interesting scenes. STILL, in a sharing relationship, regardless of the couple, there are stages that occur. It does not advance all at once. No relationship will withstand that kind of change and be healthy. Again, conventions in games make it so we can skip some of the trust-building. But the stages a couple goes through are important and they lead the story naturally. Skipping those natural steps will cause problems with readers, especially those who have experienced it.
So if the dev is fine with everyone hating a love interest (or in this case, a major character) they can do whatever they want. It's their story. But if support matters, if appealing to a larger audience than the five guys who love being cucked in the most painful manner matters, then they follow the "rules" that ease people into the major changes.
There was another story on F95 that made it feel like they were writing a cautionary tale of everything not to do in the lifestyle. Or a way to end every relationship through open relationships. It got that bad. People were pissed. They abandoned the game. That is the history of all NTR/NTS games on this site that do not follow the "rules." Like it or not, that is what you will observe if you do even a cursory scan of ANY of those games. People are fickle!