How do I get my girlfriend back?

help me a was in a relationship with my best friend she we are not together any more don’t know whats the reason she just stops talking to me whenever I ask her the reason we were very serious and we decided to get marry in future many big changes ocurred in my life just for her ans she also adjusted herself to be in relationship her parents said whoever the boy she gets marry should be having a god job now she tells her dad would kill her if she suggests my name to him for marriage in future I became workaholic just for getting good grades I m enough good to get good grades but according to her I should get more I changed my everything just to be woth her and she also but she is not now with me I want to back with her she just gets tempered if I ask her the reason for the break up I m very high tempered person as far as I know myself if I m very angry I even don’t think of anyone just do the things what I want but not the wrong things I controlled my angriness for her she doesn’t like me to be tempered I need help please help meee I m unable to concentrate on my studies just because of her and when she was with I was doing all things to keep her happy na d also was able to concentrate on my studies none of her and my friends know about our realationship I told her everything that I have adjusted and will also adjust according to u ( her ) so now what would the answer ???