> The biggest reason I don't maintain contact with people from my past is I was a much worse person in my past and I'm either embarrassed about my behavior or concerned that my shittiness is what led to our relationship in the first place.

I feel the same. In fact, I intentionally avoid interacting with people from my past since they may have bad memories involving me that I'd be resurfacing by contacting them. I've considered reaching out to certain people to apologize, but I stopped when I realized I was mostly just looking for absolution rather than actually trying to make them feel better. To me, the kindest thing I can do is stay out of their lives.