I dont know what to do?

I met one girl when I'm 17. She's not very beautifull but fine, classic. I loved her and She loved me. We talked(met) 3 month. One day she offended and left me.Resentment is me stronger I even don `t know what happened between us. I tried many times to go back but it did not work. If she loved me why she can not forgive me. Perhaps she dislikes me. I don `t know what to do I just can not forget her. I love her very much.Please advice me