For every woman who tells me she doesn't do casual sex, I make it a point to send them a formal invitation!
Ok, Ok... seriously: Most guys are going to be interested in sex... eventually. If he really cares for you, he'll wait. But to be fair, you can't dangle that carrot and say "You'll get it when the mood finally strikes me." You'll need to give him something to set his sites on. If it's when you're married, fine. Tell him that. If it's the second Tuesday in October, fine. Tell him THAT. But give him a goal. Otherwise, in his mind, he's waiting for a time that may never come.