Ex best friend problems

Alright well my old best friend dated my brother for 2 months then broke up but she was still in love with him. Then my brother got sent to a boarding school and she missed him terribly. So she told me she was gunna hook up with his best friend. And they had sex like every night even when I was at her house. Then his girlfriend found out and they stopped. But then my crush asked me out and we were dating for only a week and the day after he asked me out I got grounded for a week so he hung out with my best friend at the time all week. And my friends are comin up to me sayin your boyfriend is hangin with your bff. So I talked to him and of course he said they were just friends and he didint cheat on me. But then they were all over eachother one day and my friend told me so I told my friend to back off and then she just stopped talkin to me out of no where and wouldnt tell me why. And then I actually saw them all over each other so I broke up with him and was like cool his real understanding and then the next day he was dating my best friend and then she tells me thats why she stopped tlakin to me. All for a guy! And when I confronted her she said ew he rreminds me of your brother. So I think she wants him just cause he reminds her of my brother. But she wont admit it. And she still wont talk to me and I forgave her about everything. I really dont know what I should do cause we were like sisters and then this happened and I was super upset. And she wont stop talkin bad bout me to another ex best friend. And shes in one of my classes this yr for school. What should I doo??! Sorry its so loong just thought id explain so you get the feel.