Hi PK-
I NEVER thought I would say this, BUT I allow my oldest daughter (20 - and a junior in college) to sleep in the living room on the couch with her boyfriend when she is home on a break and he is here for a night or two. She is a GREAT student...has a scholarship...honors...and works both as a waitress and at a barn (she is an equine major) and truly is a wonderful person. 'He' is a senior physics major...and they have been in an exclusive relationship for over a year.
Much to my relief, they both have their own apartments off campus...and with their very busy schedules, I know that they have little time to see each other.
There truly is no 'hankie pankie' going on when they are here......there is no way to 'close' the living room off. And with my houseful, particularly holidays...it would be near impossible! lol
I am not sure how I would feel if she was living here...but I am sure I would address it and come up with some kind of compromise.
In hind sight, I wish I had spent more time (perhaps even living with my now ex) as perhaps I would have seen some red flags that I didn't see while only dating.
Am anxious to read other answers...
Best Luck!
michele/cat