lying?

I have this friend, we are best friends. This girl was also my best friend's ex-best friend in the past. They've only just started to come close again. One minute my best friend hates her, and the next minute they love each other:'(

Well one time it was the ex best friends party, me and my best friend didn't want to go, so we decided to make up an excuse. Well in the end, my best friend confessed to the ex best friend and blamed it all on me. Now the ex best friend had a go at me and made me cry. Now i feel as though i have no friends, and i cannot trust my best friend anymore, she's changed. Shes bunking, swearing, caking on makeup all the time:/ she thinks shes a right gangster, well she aint.