How to deal with betrayal from ex-bf?!?

Sounds like the guy is dealing with his emotions in a negative way and it is hurting you. I think your true friends will see past this, and recognise him for being a fool for the lies he is telling. When someone starts a rumor, they are damaging their own self-respect which is why it is overall a negative thing. I think he may still be dealing with hurt from your relationship, and probably has vulnerable feelings that he feels he cannot talk to you about. Guys often hide their true feelings beneath a barrier of anger.