Major regrets in my life. Lots of guilt, wishing I'd done things differently. One major one is a falling out I had with my mother when my kids were babies (I was a nondrinker). This devastated my grandmother. She relapsed after 30 years of sobriety and died within 6 months. I always believed it was my fault. My mother passed away not many years after and never accepted my apology for the ugly things I had said.
Major regrets in my life, ones I can't fix. There are other regrets of course but this is one that just haunts me still because I was never able to make amends.