It's fb, so who knows...
Why don't you introduce him to your friends? I think if he was saying inappropriate things to them, they probably would have told you...
They're not really your friends, you may think they are, but a real friend doesn't move into another's territory. It's the law of Woman kind.
He just wants to be in your life more by getting to know some of your friend.
Introduce him to some of them(:
Perhaps he wants to be more involved in your life by knowing more of your friends?
Or maybe he's just one of those people who likes to have tons and tons of friends on their friend list.
You could always just ask him.
He is looking for new talent should things not work out with you, or he is social and likes lots of friends on fb, some people like having lots of friends, bit like a status symbol.
he might just be a facebook friend whore, you know the person that has so much friends but doesn't actually know any of them, to some people they take it as a social status if they have a lot of online friends, and I think it's easier to get the opposite sex to be your friend with out knowing them, because some people will add you if they think they're cute