How to stop caring so much about other people s thoughts?

Old Counsellor once said that I have severe abandonment issues, I m always the one people betray in the end…
How can I stop caring about if people betray me. I m severely loyal but, I just lost my best friend because I heard him talking badly about me behind my back so, I got upset and just left, I can t stand why people always do this to me…
I am so alone and have no friends so to lose my best friend is just really annoying to me, he apologized but tried to justify himself that I m the one with problems. And I wanna stay strong and not go running back… For once. Cuz I always do that lol.thanks
Added (1). Sorry for poor grammar, it's hard to type on an iPhone.

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