Caused An Ugly Ending

We had been dating for about 3.5 years. We stopped dating around the middle of November because I had hurt her again (completely unrelated to cheating), but we were working on us. There was a point where she was completely done with us, she blamed herself and whatnot, but for some reason I didn't accept that goodbye and convinced her we can keep working on our relationship.Then a week later about, New years eve, I made out with a friend of mine. The next day I told my "girlfriend" that I was giving up on us completely. A couple more days after that I told her why I was giving up. Because I proved to myself that I didn't even care about our relationship anymore and I did not deserve to ever possibly be with her again. Once I told her, she hated me. She's had a tough life and I was suppose to be the person who she could trust. I don't know how to live with myself anymore, and I want to be in her life. I know we probably can never be in a relationship but I have always wanted to still be there for her always. Whenever she needed me. I ruined any chance at that. She does not want to talk to me of course. I don't blame her, but I don't want to ruin her life. I want to be a positive character in her life for her...So I didn't necessarily "cheat" on her since we weren't "dating", but that's all labels and bullshit. I caused a horrible ending to our relationship and ruined any chance of being in her life. How do I live with myself? How do I work towards being in her life again? How do I fight for her?