Why do I still get jealous when he talks to other girls?

Anonymous
I was rejected by this guy I have been talking to on a language app for the last three months. Earlier we used to talk a lot in my VRs (voice room) alone but now since our friend's group has expanded he talks to other girls a lot. Which gets the best of me & I act out. To which he once reacted “I talk to everyone in your VR why do you care if I get along with the others”? I want to stop feeling jealous and insecure about someone who has like already rejected me. But I'm failing to do so because he has been a good friend to me even after knowing about my feelings. So should I be the one pulling out of this friendship or what?
Why do I still get jealous when he talks to other girls?
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