She told me she is Unable to love me?

My ex girlfriend and i have been dating for 4 years, throughout those 4 years we had alot of ups and downs. I did not realize how much she actually meant to be until she left for the first time because of what i did. I was not there for her in the beginning, until the 3rd year when we broke up and she started dating someone else. We realized that there was still something between us, and at the moment i changed so much. I finally realized that i had everthing in my arms back than. We stated dating at 16 and now im 20. Things were really messed up, however i always loved her and never ever wanted to break up. She recently broke up with me about 2 months ago and started seeing someone else, but we been getting back on track again. Today we had , or made love, in other words. and i told her that i loved her and i want to be together, and that i changed, and she sees that. I sat her down and asked her to be my girlfriend once again with a tear in my eye explaining how great everything use to be and how happy we both were. but she says "the past makes the future." and i said yes, it made me realize how much you meant and that i want to take care of you forever, i love you with all my heart and more. Than she just told me that this is all bull ****, right to my face, and *** you, *** this and that, it'll never work, and i cant love you. I cant give you what your asking for. Yet we just slept together and spent days together prior to this incident. I try and i try and i try, but now i have to forget. How do i do so? i am so lost, loving someone that does not love me. Im tired of this, it's been over a month chasing her. she tells me she loves me, yet blows up in my face.