So weak. Quit being insecure about Darian, he's way better in the house than out of it. It means nothing if the sister chooses to cheat on him while he's gone. It demotes the MC down to just a lowly second fiddle, an alternative, a last choice. Cheating on him while he's there has so much more of a kick to it. He needs to learn what a cuck he is and what a slut his girlfriend is. She can brutally cuckold him right to his face while showing that even with him there she'd choose the MC over him. Kicking him out makes him a non factor which completely nullifies the netori, there's no stealing, barely any betrayal. It's gross, and it's super fucking weak that anyone would be so threatened by Darian that they'd want that.
Either way, dev's made it clear it isn't happening. Either move on or quit bitching, your complaints aren't productive in any way, shape, or form anymore since you've gotten your answer.