So many things.
Not taking the evidence if my step father's rapes to the police at the time when I had physical evidence to have him prosecuted. I didn't think anybody would believe me.
How different life might have been if I had been taken away from my abusive family as a child and had help and a safe home instead of living in terror for years and then having to support myself from 16 onwards.
Not being diagnosed with autism and ADHD until my 30s. I could have achieved so much more and suffered much less with self-understanding. Not that I could have done anything to make this happen so not a regret of mine as such, just a sadness. Not thinking more about what I actually enjoyed and studying/ making a career from that instead of one I have to force myself to do.
Not having much harsher boundaries with people and more self-respect. Not realising that I deserved respect and love and cutting off certain family members who had been complicit in abuse much earlier. Should have got trauma therapy much earlier in life and no resorted to very unhealthy coping mechanisms.
Terrible choice of husband and the impact that will have on my children forever that I try to compensate for but can't, of course. If I had got therapy earlier maybe I could have avoided him. Paying off his six figure gambling debts for him was also a mistake. In fact getting married at all was a huge mistake, worst financial decision ever and never again. No idea why I thought marrying wasa good idea, to anyone. Many other disastrous financial decisions due to undiagnosed autism and ADHD and untreated trauma. Too much impulsive behaviour, or me just not understanding people's nefarious intentions and taking them at face value.
I've let far too many people treat me terribly. Never again.
Ultimately though it is all a learning curve. I am trying to design a life now that works better for me and to ensure DCs will have a very different experience: early diagnosis of their autism and proper support, a stable home with just me, no step-parents. Focus on work/ life balance and save lots for early retirement, try to pay off mortgage early, happy experiences and memories. No reliance ever again on anybody, but close relationships with a few wonderful friends. Simple and stress-free life and a home full of affection and happiness.