> I have made plenty of decisions that caused a great deal of suffering - but they made me who I am.

And if you-then hadn't made those decisions, that would have helped to make you-now a different you.

Unless you value being "who you are" instead of "who you might have been" more than you care about the suffering you caused, it's not clear to me why you shouldn't regret those decisions. (Note, I'm not saying you shouldn't prioritise your values like that, especially if it was mostly you who was suffering.)

This is mostly nitpicking. I agree that there's a difference between "I regret doing that" and "I regret not doing that".