My biggest regret was pandering to family demands of helping them run their business (for no pay!) due to emotional blackmail, i.e. working all weekend on top of my own M-F full time job, and even doing a couple of hours some mornings before work. At the same time as trying to gain professional qualifications by self study/evening classes, and having two hobbies of voluntary work.
I VERY nearly lost my most serious boyfriend because of it as he was, rightly, miffed that I had so little time to spend with him, literally a couple of evenings per week of around 2/3 hours and barely any time at weekends at all! We broke up a few of times because of it, but each time we got back together. At the time, I kind of blamed it on him not being understanding/supportive, but eventually I finally had the light bulb moment that I was the unreasonable one (in fact it was my family with their emotional blackmail that I had to help in their business!).
In the end, I had to walk away from the business and had to go low contact with the family as I stopped working there and they took it very badly. When I was "free" to spend time with boyfriend (who was by then my fiance), I finally realised all the wasted years we'd suffered. We were finally free to spend quality time together, free to have more holidays, started wedding planning, etc - all of which had been impossible. It delayed our marriage and living together by several years, which in turn meant I was too old to have more than one child, which is my major regret. All's well that ends well, I'm still together with DS 39 years later! But almost every day I'm thankful that he put up with it and waited for me!
If I had my time again, I'd throw myself into that relationship and stop working in the family business as soon as I'd got a F/T job. It would have saved a lot of pain and misery along the way. It's not as if the family business was worth anything anyway - ended up having to be sold for peanuts when my parents got too old to run it themselves, and it meant they had no quality of life as they never got to retire and enjoy the benefits. I think if I'd have walked away earlier it would have forced them to sell many years earlier at a time when the business was more profitable and would have sold for decent money, so indirectly it affected them too in the long run!