To be fair this is one of the rare avns where you have to be very careful to not accidentally cheat lolonly cheats if you make him cheat. My MC hasn't cheated once on any of my main saves. There is 0% chance for this have a harem there are several point in the game for break ups to happen and more to come.
Maybe not full on sex but i would consider a lot of the erryn and mc relationship as at least cheating adjacent when you on other girls paths and not a total asshole to her for example