Most Helpful Guy
He sounds like a downright disloyal scumbag. Tell him to piss off the next time he bothers you. The real victim here is that other girl.
Most Helpful Girl
Tell him not to bother to come back at anytime because he is not welcome in your life.
You don't want to get yourself involved with a liar like this guy seems to be, will just make your life unecessarily complicated and messy.