That's the thing, players play as the main character of this game and it's on their conscience what choices they make and what choices you give to players as the author of this game, but when it comes to the MC's bride or other girls, you, the author, make the choice instead of the player. It's just that love in your understanding looks very strange if she is the bride and loves the MC, then with what logic does she cheat on him almost on the first day? You just give players a choice and people who want romance will go the loyal way and will not start a relationship with the bride's mother. I understand that this is your first game and you are still learning and your script is most likely written, it's just that your game went to a certain audience of people who like ntr or are neutral to it, but not to a vanilla audience that likes romance, etc. Again, this is your game and it's up to you to decide how to make it.
And I just don’t understand how MC should react when he finds out about the betrayal, like everything is fine, we’ll continue living?
And yes, not everyone plays games for porn, there's enough of it for pronohub. Many play for the story and get into the character's shoes, and when you write a script, even if it's fantasy, you have to imagine what people will feel. I think you yourself wouldn't like to see your fiancée cheating on you. And yes, in all games, the main character, no matter how hypocritical it may be, is always allowed more than others, and it all depends on the player's conscience.