I also have made a ton of bad decisions in my life. A lot of them, however, have occurred since this one instance; and although I've never really talked about it publicly before, maybe my remembrance of it upon seeing your question is a sign. 

My mother got really sick with cancer when I was in high school. She had been diagnosed years before and had gone through chemo and what not, but at a certain point it got much worse. I went to an "alternative" high school in which many kids were allowed to do their schoolwork online due to athletic sponsorships/obligations. When her condition started to worsen I requested to finish the year of school from home so I could look after her. I think the school was into it, but my mother outright told me no; that she didn't want to get in my way or something like that. No matter how much I pushed she wouldn't allow it and the idea fell by the wayside. 

I was home for Thanksgiving the following year and her condition had gotten much worse. She was in a hospital bed with a full time nurse looking after her in the living room. I was in a very bad state- she and I had a much stronger connection than anyone else in my own life. I stayed up for days on end sitting by her bedside just watching over her. One night, the nurse asked if I should go to bed- after I had been up for a few days with a few random hours of sleep once. I told her no, that I was going to stay up. She persisted, and I gave in, thinking I could use a little bit of rest for the next stint. 

When I woke up the next morning she had passed. It was the most horrible feeling in the world. I struggled with depression before that but it got much, much worse afterwards. I think many of the bad mistakes I've made since have been the result of never forgiving myself for going to bed that night.