I have had similar thoughts about myself: why on EARTH did I do such and such a thing?
I am finally learning through Al Anon, to talk to myself more gently. Instead of having thoughts such as, "I was SUCH a fool to do so-and-so," I'm learning to think instead, "You were doing the best you could at the time." Most of my life, I had very little in the way of emotional support, or safe, helpful people to discuss things with. Most of us ACOA's don't.
Beating oneself up over it now isn't helpful.
Over time, it's becoming easier to talk to myself in a gentler way. It can for you too.