For the first time in my life I liked this guy and he liked me, everything was moving towards a relationship when I found out that he was cheating on me and was nt a good person so I simply stopped giving him any attention so that he moves away from my life .He did move away but I didn't , I can't forget him, I'm always thinking about him. I have to constantly remind myself of the truths I now know about him. What to do?

Keep reminding yourself of what he did until you get over him, until it sinks in. How long has it been that you broke up? How long did you date?
Do other things, go out, meet other people.