First, let me say that I do sympathize with the way you are feeling - your mind is all in a whirl right now. It may be that you are afraid to truly fall in love, but I think there is more to this than meets the eye.
Obsessing is another aspect of anxiety - we drive ourselves nuts trying to figure out what went wrong in a relationship. But several of your statements really caught my attention: "It makes me angry yet more depressed to know I've ruined her life...."
Whoa!!! Please believe me that you have NOT ruined her life. She was just as much a part of this relationship as you, and she was perfectly capable of making her own choices. "...to hear her tell me I don't want her, and that she is pathetic for loving a person who doesn't want her."
Sometimes we are so willing to blame ourselves for problems in a relationship, we do not consider that perhaps there are issues with our partner that we can neither see nor understand. There is big time manipulation of your feelings going on here - and your girlfriend is likely totally unaware of this. Please give some thought to the fact that she is WILLING to let you shoulder all the blame, but there are TWO sides to every relationship, not just one.
Your feelings are stemming from deep insecurity issues and, the phrase we hear so often because it happens to be true, low self-esteem. The fact that you are obsessing over what YOU did wrong, the feelings of guilt, your concern about what she will think of you, and that you even wanted her to end the relationship all scream, "I feel so bad about myself that I don't deserve to be loved."
I'm curious as to why you "decided" to get really drunk one night - were you already feeling that the relationship was floundering? I doubt that it was this one incident that made you feel as though you didn't love her - the signs were already there.
I urge you to get help to deal with this if you can. A good counsellor will help you sort through your feelings, and hopefully get to the root cause of your anxiety and low self-esteem. I've been in your shoes, I know how it feels, and I know how much counselling helped me.
I wish you the best, and I hope you will take the necessary steps towards feeling better about yourself and your relationship.