I have two,
Staying with my boyfriend aged 15-19, he treated me like shit, cheated on me constantly (which I suspected but was in denial) and insisted on unprotected sex. He crushed my self esteem, he was abusive and coercive and had sex with me when I was unconscious. I didn't consider it rape until recently, I had pushed it to the back of my mind. I should have been out enjoying myself and had I not been involved with him I would have achieved all A*s in my a levels I have no doubt, and maybe found something positive to distract me from the bullying at school.
Going to Uni straight from school. I had had an awful time in sixthform with bullying and wasn't ready emotionally to live in a communal space with other teenagers. And I got allocated a shared room which made it worse. I'm happiest when I am making something, it doesn't matter what, I do all the DIY in our house as well as craft and painting/sculpture work (or I did before having dd) but because I was academic my parents pushed me to do an academic subject at uni and I hated it, my mental health deteriorated and I had a breakdown dropped out and didn't leave my flat for months or speak to anyone I was in such a bad place. But because their income meant I couldn't get a loan to cover even half my yearly halls rent I had to have their agreement as to what degree they would be funding. I should have pushed harder to do Fine Art, they are allowing my younger brother to go to drama school, and that makes me a bit angry still, but I know that's unfair. They were just misguided and they acknowledged that and have apologised, thankfully our relationship is better than ever since having dd. I was planning to go back to finish my degree once dd is 2, but now I just don't know, I'm wavering because I know DP would happily let me follow my dream and support me financially but he has done that for us for so long and I want to give him a break at some point, and having a well paid stable graduate job would mean he could be the sahp for a while or go back to study for pleasure in whatever obscure topic he wished. It's so difficult to make decisions, even more so with the added responsibility of a child.
Phew that was cathartic, good thread OP, it is really interesting reading other people's regrets and insights. I don't know how to advise you on your dilemma without specifics, but I would keep in mind that you can't let past regrets instil a fear of making decisions, keep in mind what you can learn from past mistakes but don't just pick the easy road because you are scared to take the unknown path.