I feel you man. I've struggled with feelings of guilt for a long time. Sometimes I wonder if wanting to apologise is just a selfish desire on my own part, so that I can be forgiven and feel better.
Realistically, having cut off contact with some of the people I feel guilty towards, I find it hard to believe that contacting them would be anything but selfish. Most of them have moved on with their lives, and it would probably only hurt them if I brought up the past.
I've tried to put the past behind me and focus on becoming a better person, but in difficult times there's always these feelings of guilt and doubt.