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I would say that he is jealous, that he didn't get from you what he wanted and thus said ugly things about you. Some men and women do this after the break up, just to feel better about the situation and about themselves, to boost their ego, as it does help emotionally. Others when they break up, conclude that they are different, think of that as a good experience and move on. I would say that he is immature. Him trying to date them is really an act of finding a rebound. That's what I think about the situation you have described.