My ex-girlfriend is being weird.please help.?

im going to add as much details as i can,so this might be long.i started being friends with this girl named yasmin last year in april.we remaned friends until she asked me out this september.we talked on the phone everyday.on haloween she dumped me because she said we dont hang out outside of school enough.a day later she went out with her friend griffin.they only went out for a week.then they broke up because he was being a jerk.btw yasmin describes all her past boyfriends as''jerks ,Dbads,a**holes ext.''so she asked me out a day after she broke up with griffin.she is emotional.if she sees me talking to another girl she freaks out.she will givwe me a mean look.and then walk off really fast.(this is at school of course.)one day she will say im her best boyfrend shes ever had,and another day she tells me im being a jerk.a week ago we broke up again because i wasa being a jerk.i never say anything mean or do anything.all her friends say id make a great boyfriend.so today her friend cara told me shes going out with josh.(yasmins friend from elementary school,and he goes to a diff school.)my heart is torn.why is she being this way?oh and i told cara hes probly a jerk.and now shes mad i called him that.