What can I do to get my Ex-girlfriend back? When I stop calling her she wants me.. I can't help calling her...

I was with my ex girl for 2 yrs 10 mths and have been trying to get back with her for 6 mths! We broke up cause she wanted space, a wk later I find her with some guy! I would call her constantly because I was shocked! When we were together she was nvr like this I couldnt believe it! I beat up the guy, even then she went back to him! They broke up after 2 mnths and then she came calling me back even after all my constant calls..The longest I went without talking to her was 1 week! So then we had started talking again, n going out pretty often, then she says something like "Remember when we were together, I never had a best friend? Well im only 20 and I want to have fun with my best friend(girl), so that when we have a family n get married(she said shes sure), I feel she'll be there for me."I said ok, but I feel like im just waiting! She always says she loves me n dont worry theres no one else. She alwys calls sayn she misses me when I dont call. When im there she takes me for granted! ?