Messy break up and it's my fault. How to deal with the guilt?

I have caused someone great amounts of hurt by dragging out a break up. We were together for 3 years, throughout which I struggled with depression, and split 6 months ago. Since then, we have been on and off. I have been indecisive, anxious and just generally confused. I feel that this person hoped that if i felt better, we would reunite. I hoped this too. I know a lot of emotional energy was invested in me, and I feel all I have done is ripped this person off. The guilt destroys me. This person has recently indicated I should go to hell. I agree. What is there to do when it feels impossible to forgive myself?