Our DS21 is the 'rebel' difficult one of the family. I have DS18 and DS23 too, but DS21 is the only one with a GF. He is often out meeting up with her and brings her back to the house very occasionally.
He does ask permission and we compromise by saying she can come in to eat dinner [they seem to exist on take aways!] but only in his room, which tbh is what they'd do pre-covid. She stays there for an hour tops and then catches the bus home [we have stopped offering to drive her home].
Should we be stricter or, as an adult [albeit living in our home], is a compromise reasonable?