Sometimes I think that I might hate my best friend.
Are you serious? Why do you hate your own best friend?
She changed her attitude towards me when I got a boyfriend.
If you really think you can't remain friends with your best friend, it's ok to end it instead of making it toxic. Hopefully your friend will understand that as well.
Shut up, I will make a scene in the middle school if I don't get what I want.
You sound like you're helping to make this friendship toxic when you speak with people just trying to help you that way, especially since I am agreeing with you. You may need to step away from your friend and stop hanging out, as it could be considered an unhealthy friendship.