Healing from my past relationship

I got broken up with a few months ago for a reason unknown. He just said we weren't compatible of which is not true but at that time I accepted it. He went on to rebounding with someone else a few days after as if she was already in the equation before he dumped and funny enough he wanted to marry me. How do you go from being excited to marry someone then dumping them for no reason to rebounding? Every time I think of him or any man I get so mad and disconnected the possibility of dating every again. He was my first everything and he disappointed to the extreme. And now, he wants to try and be my friend. What should I do?