How can I help my friend?

So I have this friend and she has this other friend which was her best friend that got mad at her for dating her ex boyfriend that she loved for like ever. she got so mad at her that she kicked her x boyfriend out and her best friend out of her house she loves this boy and her best friend knows it but she still went out with him and now they broke up but she didnt break them up he broke up wit her because she gave him letters that she wrote ever since they broke up. But now that they are broken up she feels better but she dosent like that the reason why they broke up was because of her even thogh she loves him. What should my friend do,She is all broken up about it inside and she wants him to be happy.So I didnt know what to tell her so does anyone know what to do she really needs help.

I would really like to help you, but I didn't get who was who and etc. Maybe I'm not quite good at English. Sorry(