Heck, when it comes right down to it, there would be nothing inherently wrong with him just wanting to have you as his late night booty call...... IF he was honest about that and you were okay with that. For you two to be dating, and then him to suddenly only call you up when he wants to "get it on" (Are the kids still saying that these days?) is NOT okay. As others have said, you should just reiterate that you are looking for a relationship, not a hook-up. I wouldn't necessarily say that right off the bat. Instead, as others have said, when he calls up for a late night hook-up, you just re-direct for an actual date. If he keeps refusing and/or keeps just trying to hook-up, then that tells you all you need to know. Then, that is a good time to tell him that you appreciate the time you did share already, but you are looking for something serious and not just an F buddy. No harm, no foul, but you need to move on. Good luck to you either way.