How should I get my ex-girlfriend back?

Hey,I am Harshveer.I had a girlfriend whom i loved more than anything in this world. Although we weren't together for a long time but we both were dating since December 2010 and we began our relationship after knowing each other in May.She was good for the first 2 weeks but after that she started ignoring me and she started missing her ex for a reason that he was sending her some messages which were really romantic but I knew that he copied them from a site. Anyways one day she called me and told me she likes me very much and she likes her ex too and she can't come to a decision whom to choose. I told her that I love her very much and she said she knows that ,that's why she isn't leaving me.But after 4 days which is today ,She sent me a message through someone else to tell me that she is with her ex now and I should move on. My heart was broken and I cried like hell. I felt like nothing is left for me now. Still i am crying in pain but she doesn't care. All I want is her and nothing else. Is there anyone who can tell me what to do? Please don't tell me to move on because I can't ,if u have ever fell in Love just tell me how to get her back???