What do I do when I got betrayed by my best friend?

Ok, my best friend or ex best friend met this guy on this christian internet thing. They started talking and stuff and just so you know she was 18 or 19 at this time. After about a few months or so of talking on the computer and the phone he told her that he wanted to come on a bus to see her. She was like ok so he got the money and rode on a bus for like 10 hours and they finally meet..Ok he stayed here for like a couple of months and I liked him he was good to her at first then he lost his job here and had to move back to his home.After awhile he quit calling so much then he cheated on her and well she broke it off with him. She thought she loved him but idk..Well about almost a year later she started calling back again and she told him that she was only going to be friends with him and he agreed to that, but then he quit calling for awhile and you now we never really talked about it much anymore..Well ok here is the betrayal part, I called her one night and we were talking about stuff and I was like got any new news or whatever and she was like no not really and I was like ok.Finally she decided to tell me and she told me that they had been talk for a month or two and she didnt want to tell me cuz she new how I would react..I was like thats not the point we are like best friends we telll each other everything..Then she told me that he was there and staying with her and she is like 20 and still lives with her parents,but she got married at 18 they divorced. So this guy is back and she told me that she wasnt going to tell me..I mean what do I do? She betrayed me best friends dont do that to each other..HELP!!!