I don't know if you tried all the dialogue options in the lagoon at night, but that's where to reach an "agreement" after "being honest", that's what bothers, in that agreement you can choose to share it with the monsters or keep it exclusive for you ... if that option had not existed, my complaint would not exist ... only that ... the game gives options that later are useless ... it would be understood as an alternative route, but if you do not advance this you get stuck ...He tells her after catching her cheating and she never does it again.
Sorry to say but he is cheating on her every time he fucks one of the girls.
Sorry to say but if you can't handle that then this game and most other games will not work for you.
She mentions what you say but still gives you those "options" that no matter what you choose, she ends up deceiving you: Yes and it implies that if you hadn't done the crazy thing to transform yourself, I would continue doing it every month or two ...