In my experience, when a man is REALLY interested, he'll stay til whenever or want to stay the night because he doesn't want the night to end...too busy having fun, having sex, talking the night away, and spooning to realize what time it is. Or if it's at his place, he'll invite me to stay the night and even try to talk me out of leaving if I say I have to go at a certain time.

By your own stupid logic, the woman in this scenario should have been totally okay with OP saying he has to leave at 10pm. Maybe he does want to "stay til whenever", but can't because of an early morning, as stated. Instead of her (and you) assuming he's just using that as an excuse for a quick fuck, she should have been fine with him coming over and if the night was going well, invited him to stay overnight.