Sorry to say this, but you were used as her rebound man. She still loved the other guy when she was with you. She spent time with you to either get her ex jealous or to keep her mind off of him. Rebound relationships don't last long and 90% of them will break up at some point. You were convenient for her at that time. So move on and if she ever came back, don't get with her again.
My girlfriend had a boyfriend before me and he told her "I don't love you" so she went out with me. She told me she loved me, and we hung out. But then she went back to the boyfriend that never loved her. What should I do?
Yeah, you were PROBABLY used as a rebound guy. I honestly think that you should set the facts straight to her and tell her what you think
Break her heart
Do? There IS nothing to do other than move on. They obviously have 'something' going on between them no matter what she told you. She has moved on .. So should you.