I've been debating on whether or not to throw in my 2 cents here for the last hour or so. I'm coming to you from a completely different perspective.
A lot of you know that my only child died in March of 2004. Before he died, the end of Shane's apt. lease was coming up within a couple months & I literally begged him to come back home. I knew he wasn't doing too well financially & morally & I just thought it was better for him to be here. His choices were to come back home or find a room-mate. I was very hopeful that he'd come here.
Yes, Seth & I enjoyed having the house to ourselves. And I worried less because sometimes "ignorance is bliss". (I married Seth when Shane was 15 so Seth was not Shane's natural father but he loved Shane as if he was.) But we both agreed that we wanted him back here & that the rules would have to change from what they were before he moved out to go to college.
GB gave you some excellent advice. We couldn't have given Shane a curfew but I would want to have some idea when he would be home. If he was going to be late or not come home, there are cell phones. GBs - you might think your mom was sound asleep when you came home but I guarantee you that she wasn't - her real sleep began when she knew you were home & safe!
Shane always stuck his head in the bedroom door & let us know when he was home & that relaxed me.
T- what will make you most comfortable? Are you a worrier? If so, then David needs to do what he can to minimize your worrying! He probably won't be around all that much, anyway. The dynamics of a parent/child relationship really seem to change once the child has been out on his own for any length of time.
I hope you allow David to come back home while he needs to & embrace the time you have together.