My friend cheated me and told my brother dirty jokes. My brother said my friend was a pervert. My friend is a girl. I'm my sister, and my brother ignores me. What should I do?

Just a personal opinion, after all, I have never experienced it. The first thing you must do is to isolate your brother from your friend. Secondly, I think you must find a chance to have a good talk with your brother and find out the situation. The biggest fear is that your brother will have a psychological shadow (if it is really serious, it is recommended to consult a professional psychologist). Finally, I think you should consider whether to talk openly with your friends about this problem. On the one hand, you should find out what she thinks of your brother and consider whether you want to continue to be friends with her.