although i was the only girl he chased after when we first met, he has since gone after other girls
You want him to chase after you forever? get a grip, he's not going to be hung up on you forever if you're not interested in him.
But this is all based on the word of a mutial friend -_-
Seriously this sounds like you're sorta over reacting to hear-say. Why dont you hang out with him and find out yourself what he's after (he'll soon let you know).
Looks for it wherever he can get it.
Don't lose contact with him if you think you have a good friendship with him. If you don't, what is the point in keeping contact with him?
If he asks for sexual stuff when you are not willing, obviously don't do it. Stand your ground. And if he really wants you, he'll learn to live with just you.
But Leopards don't always change their spots.