How can I not be jealous?

So I broke up with my girl a few weeks ago and I found out she got another man. When I found out I got extremely jealous and angry. I don’t like those hurt feeling every time I hear about them and it makes me feel awful. I don’t want to be jealous I want to let go and move on. I keep telling myself “I don’t care I don’t care” but I really do care. It’s like a sick feeling in my gut. I wish I didn’t feel this way. How can I truly not care and let go?
How can I not be jealous?
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