Can someone help me get my ex girlfriend back?

Ok me and my girlfriend have broken up 3 times 1st time she broke up with me but we got back together and acted like it never happend 2nd time I broke up with her then we got back together and I promised everything would be different and after hat we were doing great but when we came back to school she wouldn't hardly talk to me then she seemed to be mad that I was talking to this other girl but the other girl is one of my bestfriends and then she finally broke up with me and said i wouldn't talk to her but I tried so hard to talk to her she wouldn't sit wih me at lunch that week or even come over then but I begged her to come home with me so we can work everything out she said no then we started talking about it some but she wont sit down and talk it out with me why is she acting like this? I just want her back and out of all the girls I have dated I have never tried so hard to get a girl back before I really care about her can someone help me please?