I've already said what I thought the appropriate tag would be for that scene: group sex, which is an adequate content warning that the game where human women join a goblin warband as harem girls isn't going to have those women limit themselves to one partner. It's not cheating if there's no expectation of monogamy in the relationship, and the game makes it clear from the start that there's no expectation of monogamy for any of the characters. Hell, Rhenise is technically still married and nobody batted an eye when she joined the harem. (I still wouldn't say the cheating tag makes sense in her case, as her husband agreed to going their separate ways, they just didn't do whatever legal formality counts as divorce in the game's society.) It's only once a scene finally gets added showing one of the women take other partners—a type of scene that we already knew from earlier dialog was coming—that people start shouting for some kind of adultery tag in the lighthearted comedy game where the relationship dynamics are such that adultery and all the uncomedic drama around it isn't part of the picture.