Why would a man who won’t marry me get jealous when I move on?

I had a guy assume I was playing games when I said I was moving on and he told me for the second time that he was seeking a wife, going on dates and would never marry me and I took his advice when he said; 'Do that;' to start seeing other men, not to make him jealous, just because I too would like to fall in love and be married one day and he's told me twice that he wants marriage but not with me and I accepted it and I have decided that I am now ready to move on. Once he realised I was serious and that I really have met two guys and I'm planning to pursue other men, he's seeking me out to openly act jealous and unhappy.

Is it about power, where they don't want you themselves, but they don't want anyone else to have you either?

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I'm not being bitchy or playing games, I genuinely don't get a lot of people's behaviour a lot of the time.
Why would a man who won’t marry me get jealous when I move on?
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