Hmmm, I have to disagree here. If they are paying more or less fair market value rent and house rules allow one person (you) to have overnight guests, even those they are dating, I think it is wrong to now allow that to go both ways. If they are only paying a token rent, OK, maybe I see your point. I disagree---it is not just semantics. Just as the adult daughter has no right to demand to know who Mom is dating, or how long, or what the status of their relationship is, she has no right to tell her mother she cannot have a boyfriend in her own bedroom behind closed doors. It is considerate of the OP to take the DD'S feelings into account and give her a heads up about a possible overnight so that the DD can choose to not be home if she prefers------heck, that is already meaning OP has to plan an overnight with her boyfriend in advance, no spur of the moment plans. For full grown adults. That is above and beyond as is.