Why is he suddenly jealous now that I’ve moved on from unrequited love?

I was completely in love with a friend for two years. I doted on him and openly admired and loved him and he took me for granted and started bragging about dating and sleeping with other women. Then suddenly I realised after some time had passed, that this wasn’t a healthy situation for me and I ended our friendship respectfully and honestly and told him I can’t be friends anymore and why and mentioned my plan to start seeing other men in a few months, when I graduate from tafe. Now he seems hurt and jealous. I genuinely don’t understand this. He said himself that he loved me at first sight and always like a sister and that wouldn’t change and that he’d tried to force interest to kiss me and try to date me. That it was basically a game when he did that and proposed to me. So why is he upset all of a sudden?
Why is he suddenly jealous now that I’ve moved on from unrequited love?
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