Relationship Problem. Forget her past!

I am 21 years old.. I love a girl by my heart and madly in love with her.. To me she is the best girl who can understand me.. I can do anything and everything for her... I met her since January, 2017. I found her amazing and the best one for me ever.. Even I can marry her now.. She also likes me and wants to live with me.. May be she also loves me.. But she has an ex.. And he continues to call her frequently... Everytime he calls her she starts crying and becomes very weak... I tried lot of times so that she can make herself out from these things.. But at a certain point of time she receives calls from her ex and starts crying.. She spent 5 years with that boy.. But at that time she also made relationships with others and they had gone through several breakups but still they managed to leave together.. But now as I am there in her life she can't leave me and also she can't forget her ex also.. She is in severe confusion now... I think she loves me too but can't forget her past