Warning: this may be long. The end happened a month ago, but the destruction of a 5 year friendship isn't something you "just get over".
Anyway. So "S" and I met at the beginning of 8th grade. She immediately liked me. A special greeting like that was very refreshing to me after the bullies I had encountered in 7th grade from my previous school. My name is the same as hers, and S has a twin, so S and I referred to each other as "name sister".
The school I started in 8th grade was small, so I spent most of my school days with her, and her twin, but I wasn't close to S's twin much. We had a ton of inside jokes. We also went special places together (my mom, her mom, her twin, and of course her and me) over the years such as theme parks, aquariums, museums, festivals, etc. We were extremely close to each other. We trusted each other completely and we told each other our secrets. I was aware that S had a friend, "V", who she had known for over ten years. But V moved away, so I didn't know her. I never felt threatened by V. Friends have other best friends.
In my junior year of high school, V moved back to our city. She went to our high school. But I still didn't know her because I did the online schooling. Gradual changes were apparent in S. She stopped wanting to hang out with me. She avoided me. We got into fights, and all of this is very out of character for S. She was a great and understanding friend. But all this was gradual, so I thought it would be possible to fix. All of a sudden, S claimed that I was "too sad and annoying". And that our texts "we're on repeat". I have depression and anxiety, so I accept that I might have been "too sad". But I fixed it. I also fixed the "repeat texts". But she still repeated texts, and killed our conversations.
She stopped putting in effort. She blamed it all on me. She complained about V kicking her dogs, about her twin, about her parents, and other stuff. I mentioned that she complained too much. She made no effort to fix it.
The last straw was near graduation. At practice, I whispered in her ear, "we need to fix this". She proceeds to yell at me and make a show in front of V. Fast forward to Grad Nite. For this, we went to a theme park the night before graduation and stayed in the park all night. She made childish comments all night such as, "V, you're my FAVE. Only you can have hair ties from me." Ok then. I got sick before we went on our first ride, and she just leaves me alone and didn't even follow me to the bathroom. Then she calls my mom and tries to defend herself by saying "Well I didn't just leave her there!"
I got better and still had a fun time with other people. At the end of the night, we started heading towards the busses. The whole group leaves me alone and I get lost, not knowing which bus I was supposed to be on. I call S and she doesn't answer. I only had her number. Finally she does and says "we are in the store". What fucking store? There's a million of them. Finally I find them, almost in tears, and start yelling at S and V for leaving me. They ignore me and walk away.
So that was it. No more of those bitches S and V. I sat through graduation and now I have no contact with S.
S's twin felt bad for me but there wasn't much she could do. Also, V is overweight, I'm thin, and she shamed me because I'm skinny. I'm not "too skinny". From what I heard, V is apparently jealous of me because I'm pretty and thin, and because S liked me so much. V is also abusing S. She's isolating her to only have her as a friend, while V has three other best friends.
TL;DR: Best friend of five years turns on me because she was manipulated by her other best friend because that girl is jealous of me. Also, she is isolating S from other friends.