Friendship issues am I wrong? Long thread

This might be long but please listen..venting.

Hey so I've been friends with this girl since middle school I'm in my early twenties now. I consider her my actual best friend..we literally talked to each other almost everyday up until senior year of high school in 2015 our conversations decreased a lot all the way up to now, now we don't talk at all she only hits me up when it's convenient. We definitely haven't talked much since 2016. One day we planned an outing with another friend to catch up but I wasn't comfortable with another friend she was bringing I decided to suck it up because that's my best friend..I told her to let me know what time we're meeting up and she never told me later on I see her on social media with our mutual friend and the person I wasn't comfortable with that kinda made me think like wow? Today as of now we don't talk at all..she works and has work friends and other friends I'm totally okay with that I'm not a selfish/needy person I go to school full time we both do our own thing.. but I will always make time to talk and catch up I sometimes text her and I don't get replies till days later or none at all.. I'm actually really hurt by this now that I just seen her out with other friends that we both use to be close with.. and those other friends are the ones that stopped talking to her once before for 2 years over a issue and now they became friends I stopped my friendship with those other two because of her..I feel stupid in a way that I use to tell her everything.. a lot of my friendships with other ppl ended bc I chose her side always and it's like a feeling of regret? In our friendship I was never disloyal..I didn't do any wrong In our many years of friendship I don't know what to go..Any advice? Am I wrong for wanting to cut all ties? Because that's literally what I'm about to do