Lots of good advice on here already but thought I'd add my opinion. He is very lucky he has a nice face. Because of this fortunate genetic fact, he has been able to sail along, having sex with who he pleases. And because we are genetically programmed to mate with a good, fit, even-featured specimen, you have fallen for his pretty package. But watch the ducks. The male chases the female. She runs away. He keeps chasing her. She eventually lets him jump on her and they mate. That's nature. Then he goes off and feathers some other bird. This man seems to be a very base creature indeed- bowing to his most basuc urges. He is really no better than a duck looking for another duck to jump on. I wouldn't be flattered by this. As you say, he would probably fancy a nun. But his habit is being fed by you, and as a result he wants more. If one of your kids wanted to eat only sweets, all day every day, would you let them, because they're gorgeous and lovely? This chap needs to learn that women should have a better place in his life than as something to shag. You would be doing him a huge favour by explaining this to him. In nature, sex is for reprodution; men are programmed to spread their seed (especially when young and fit) and women are programmed to have babies and nurture them. I would hope that we are a bit more developed than the ducks and dogs, and can have meaningful relationships than include but aren't obsessed with sex.
Let him go, and find a man who really likes YOU, not your privates.