But that's just how most harem games are.
Threesomes, foursomes and more are a big parts of most harems as most people wants to see a man covered with women who wants to please him. Yes it does include some lesbianism, but that's just a side effect of all of it. At best you could ask to "skip" it, but if the scenes has important to the story(seeing as in this game she is in a relationship with Robin) you might miss story beats, but that's the dev's story at the end of the day
And I said it before and I'll say it again, devs makes the story they want to make. So if a game doesn't have the content you want, you shouldn't force it to change, you should look for game that does. I don't ask a game where lesbianism is not a thing to add it and I don't expect the dev to change the game to fit my testes.
And if it bothers me that much I just leave the game, I haven't paid for it and I don't lose anything by dropping it(there are plenty of games out there).