Lost

A few weeks ago my girlfriend broke up with me saying that she gradually lost feelings and wants to have a chill relationship rather than a committed one. I didnt take it well in the first few days, I cried multiple days and contacted her multiple times to try to grasp the situation. It was hard to understand and to accept it because we went through two years together. We had many up and downs together and I genuinely thought we had a future together because she thought so too. I catch myself reading our old texts, letters that she wrote me and pictures of us together. It breaks my heart and I'm slowly accepting it and trying to move on, but I cant. I dont know what to do anymore. Theres a part of me that questions why this happen, was I not good enough? was there another guy? and a little tiny voice in the back of my mind keeps telling me that "youre not good enough for people, this girl wasted her time being with you and no one will ever love you again, you will be all alone." The other part of me is forgiving her and hoping for that text or call from her that made a mistakes wants to get back together. It really hurts, she seems so happy and doing okay and its hurting me more to see that. i dont know what to do, please help me?