Why does my girlfriend get so mean after being so nice?

Oh jeez, you did a right thing by breaking up with her. You wanna be with a person who makes you happy and doesn't treat you like ****. You obv deserve better because in relationships, you can't give 99.9% and she gives 1%, it's gotta be both 100%. Go have fun at the festival with your new date, hopefully she'll be better than you ex!