here's my first thought:
why are you friends with this woman, exactly?
i would say your man sounds alright; it's more the friend who is the problem. if you sincerely feel she would screw you over, and there is no point talking to her about it, i would say break-up with the friend, not the man. life is too short to spend *any* emotional energy on a petty, useless, friend, that you can't trust.
i think you have to decide if this is
1) insecurity talking - you are worried she is somehow more attractive than you, in which case you should work on yourself;
or 2) intuition talking - you realize that your friend is skanky,but don't have the heart to dump her. if this is case, get the heart, and get rid of her.
if your relationship with your guy is a good one, you can just tell him, without cattiness, that she is simply a waste of your time and you have better things to do. if he continues to ask about her, you can tell him he sounds like a chick looking for gossip.

he may just be trying to get a rise out of you.
in any event, don't worry too much - if he is worth your time this will work itself out. it honestly does sound like the larger problem is in your friendship with the girl.
just my 1.4 cents

good luck!