Is it normal for your best friend to be a complete b!tch?

Hi! My name I Jane. I guess I just want help with this situation to figure out if I'm the wrong one or what.

I have a best friend who's name is Dj. She's actually my first cousin as well. Recently she's been going through rehab for coke addiction. I told her many times not to do it, because she was afraid they would keep her away from me because I was always wasted. I realize how fucked up that was now.Anyway, during that three week rehab stint she avoided everyone, including her boyfriend, Cleadus. Now I always thought he was a hottie with a naughty body. You know,a cutie with a button booty. But I never thought I'd betray her. To my everlasting, sexy shame, I did. A few days later he told me he was sorry about this. Me. The drugs. The clown. Everything. I was devastated. At what I don't know. But we were all weak. Insecure. When she came out of rehab, the bitch acting all high and mighty told me that I was a drunkard and needed to get off my ass and do something about my life. Now I'm not a violent woman, but I threw that farberware pan filled with last nights fish dinner in her like I was in Mexico and a coyote was trying to steal my mariachi 8 track. She took it like a man and came after me. I don't remember how it happened, but her boyfriend arrived at the scene and broke us apart. At which point I kissed him and told her we would be together forever. He stopped, stared at me and then ate a piece of fish in her hair, and walked out with her. We haven't talked since 1 week. I used to talk to her everyday before rehab. Now I'm nothing. Treated like dirt. I don't know how things got so bad. The thing is she made my ex cheat on me with her 2 months prior to all this. Sure it was painful, but the man was eyecandy. I UNDERSTOOD. SHE DOESN'T. I guess what I want to know is who's wrong here? Her boyfriend was hotter, but does it matter? What about the clown? He's been calling. I don't know what too do anymore.
Is any of this normal... babies?