Stabbed in the back how many more times?

so this girl she used to be my best friend my sophmore year beacuse her best friend dumped her beacuse she didnt like her boyfriend... well neither did i but i still stuck with her cuz thats what friends are for right??and now that they broke up almost two years later this girl her ex bestie wants back in her life and now she totally dissed me.. so last year me and her brother started talking and she went crazy beacuse of it and got madd... well this guy i had been dating a few times but was really close with and she knew it she is now dating him my ex and you just dont do that... well she doesnt think anything is wrong with it and me aand him just told each other we love eachother... and she knew him first but i dated him before i knew her and when i knew her and she was cool bc she didnt like him now this and she thinks its cool what should i do and say??