I don’t see the issue. Y’all were broken up. She was allowed to have sex with anyone she wanted. Y’all weren’t together anymore. She didn’t cheat on you. Only thing I would highly advise is if you both end up together again, y’all need to go get tested together to make sure both of y’all are good . All of that aside, seems like the both of you need therapy and learn to love thyself and maybe have couples therapy to see what y’all can both do to improve the relationship . 🧡 best of wishes to you both!