I regret not marrying my late husband sooner.
I regret not putting my foot down harder over his interfering ex.
I was on my best behaviour all my married life, so as not to alienate DH's adult children. After he died and I had the funeral to organise, I again bit my tongue over some matters and agreed that the ex could come to the funeral to "represent" them during lockdown. (It turned out that it was her idea. Man Number 4 dropped her off and picked her up.)
At one point, DH's DIL informed me that his ex was 'devastated' about his death. NB DH left his ex when he found out she'd spent the night with her 2nd man, but she managed to convince some people that she was the victim. DH and I were married 24 yrs.
3 days after the funeral I was woken from a Diazepam/Zoplicone induced sleep to find her on my doorstep. I thought she was just there to give me her condolences, but she wanted to know what I was doing with his ashes. I later realised she had wanted to convince me to place them in a location of her choosing.
I regret not telling her to get lost then. Instead, I finally lost it a couple of months later and the kids have gone NC with me. (No, I don't blame them. I was out of order.)