I have a jealousy problem

Honestly I’m not an insecure girl but for some reason I hate my boyfriends ex. Like it makes me so angry every time I think about it and when I see her hang out with people I know I get annoyed!! My boyfriend and her don’t talk and he’s the most amazing man but I can help but get such a bad feeling! I’m not sure if I’m alone in this but does anyone have any life lessons or sayings they say to themselves when they start feeling jealous! I’m trying to be more confident:( any advice?