How do i win back the girl of my dreams?

About 6 months ago I met a girl at the local gym. I had heard earlier she was engaged and had three children with two different fathers. We got talking and she explained she had broken up with her partner and he was soon to move out of the house. We got on really well and over three months we got together. I held back my emotions because I did not want to scare her away as she had just finished in a relationship. She said wonderfull things to me all of the time and put me on a pedestal which made me believe everything was going fine. About 6 weeks ago the contact was getting less and when I quizzed her about it, she replied, you told me to not get hung up on you too much and that she was thinking about me all of the time and consumed her. I have since found out she has met someone else. When I asked her about why she had done this to me, she told me she thought I was not into her. I have explained everything to her about not wanting to go full in and scare her away but she tells me its to late and she loves this guy. Im broken and miss her dearly and dont know whether I should try and win her back or move on. I have told her numerous times about how much I want her back and how much I miss her. Have I just dropped the package of my dreams out of my hands? I dont want to give up on her but is it a hopeless task? Broken!