What to do about your friends dumb bf

listen

I had  a friend and she was dating this guy that was dating other girls behind her back and those other girls just happened to be some of my other friends and when I went to one of my activities  after school they were talking about her bc her bf just broke up with one of them and rubbed it in her face that he has found someone new . It just happened to be my friend so my group of friends that all ended  up dating the same guy and asked if I knew who this girl they're ex is dating I said yes so the told me some things my friends bf did  to them and what he is going to do and I told my friend and tried to warn her but she was so caught  up in him she lost all sight in reality. All I wanted was to not let her get hurt ,but she is no longer my friend she said I was making up things about her bf , but I don't know why I would do that . Honestly if he hurts he now I don't know what I'm going to do . Should I confert her ? Should I tell her I told you so ?  She is a good person dating  the wrong man and it makes me sick .