My ex wants to be a close friend of mine, but when we broke up he was a jerk at first, should i?

I was dating this guys named Zack for 3 months and we were fine, then i found out he had been cheating on me with this really... larger... girl. who he knew i hate so he didnt think id find out. after we broke up over it, he started goin around telling people i'd slept with him and that he never loved me and that he was only with me because i black mailed him into it. we're only 15 so no, i have NOT lost my virginity and it bothers me that we would go around telling people things like that. alot of people lost respect for me for a while before i had sorted it all out and now he is talking to me like none of this happened. (and by the way WHEN this happened he was telling me he would never do it again and then doing it the next day) he says he wants to be a close friend i can cry too. (hes a sappy guy...) but he always is dissing his friends to me. should i trust him? what should i do to get him off my back?