I find that sort of thing can just do your head in, especially because even if we had done/said/been whatever, we've got no actual way of knowing how things would have ended up ...

So in terms of processing regret, I'm not sure that I do ...

There are some things I would like to have done differently - but doing them differently may or may not have meant that I had a better - or even different - end state of play.

Some things I perhaps would do differently anyway (spending more time with loved ones before they died, not doing or saying things which ended up hurting people I love, whatever) but flaws and all, the bundle of actions and inactions and wins and mistakes that have happened along the way have made me "me" ... and so on I plod ...