Advice!! PLEZ?

My best friend that calls me big sis is in major trouble......Her bf cheated on her with her ex bff and did stuff with her other bff and she still wants to give him another chance and he stood her up 9xs!! She keeps getting her ova him it pains me to see her like that...me and another bestie talked to her telling her dont run back to some1 who she knows who would hurt her....Bt she keeps standing up for him IT REALLY PISSES ME OFF! HE cheated on her for the 3rd tym! I told her that he tried to kiss me and she wouldnt belive me until he admitted and when she found out he did sum thangs wit our othr sistr n talked dirty to me all she said was hes a boy he should be horny......IDK WAT TO DO ITS REALLY PISSIN ME OFF