My ex girlfriend is flirting with my friend?

My ex girl friend getting close to my best friend and keep avoiding me and my friend use to talk bad about her. This made me jealous,and I feel like so bad.Like she is slut easy girl.Tell me what I do to stop her going with wrong guy,and she don't talk much with me anymore,its hurt me how can I overcome of this problem ,please help me out.
My ex girlfriend is flirting with my friend?
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