Fine. This is how it goes. Is it real or am I crazy?

My best friend is my FP. It stands for favorite person. People with borderline personality disorder unconsciously develop FP attachments. Now, my best friend and I have been very close. There's this friend group that my best friend is a part of, but I'm not. It hurts me, because his friends are kinda mean to me, and keep me out of things. There's this girl (let's call her Anna) who doesn't talk to me, and I felt from the very beginning, that it's because my best friend and I are pretty close, and she doesn't like that. But because I have BPD, it was hard for me to understand if it's just my paranoia, or if it really is the case. My best friend would never believe me when I'd tell him that. Another girl confirmed it for me today, as she has had a similar experience with Anna. She said "Anna doesn't like people who are friends with * my best friend's name *. She does the same to me." I was shocked to hear this confirmation, as it meant I wasn't crazy. I was always told by my best friend's friend group, that my "behaviour" wasn't up to par to be socially acceptable. Now I know they're just gas lighting. I'm just extremely depressed that my best friend refuses to believe me when I tell him that his friends treat me poorly. I cried again today because I don't like being treated like this. And then to be gaslit about it. It's mental torture. Today I went over to her to greet her in general with the other people she was sitting with, but as soon as she saw me approach her, she got up and turned her back to me, pretending to get busy with other people. It's a small gesture, but it's profound. I feel so alone. Despite having a best friend, I feel alone. I feel he thinks I'm jealous of her and making things up. So he doesn't cut them off. He doesn't take that stand for me. And because he doesn't, it only encourages his friend group even more to treat me like shite. I'm so exhausted. I don't want to get into a fight with my best friend again over this. I'm so scared of losing him. He's my only real friend and I don't wanna lose him over some stupid people that shouldn't matter. But again, I think I deserve to be stood up for. I deserve for my best friend to stick up for me and to cut off these abusers because they're clearly not good people. I'm not sure if my hurt and anger is justified, or if it's just my BPD acting up, I can't tell.