Op, why would you want to stay with a cheating, lying slut?
Keep your self respect and dump her. If you 'forgave her' she'll do it again but be more careful. You'll never be able to trust her.
Have some fun with it, say you spoke to 'malc' or whatever he's called, he said he knows you quite well.... make her squirm, see if she confesses, tell her he's bragged to all the guys about what a slut you are then dump her ass!