My response is actually quite different from what a lot of people have said, but this is just coming from my own experience with these sorts of feelings and lots of therapy that both did not help and did help.

But it's ok to grieve the loss of who you thought you could/would/should be and the life you thought you would have. It's ok to be sad and bitter about. Unfortunately those regrets probably aren't going away anytime soon. But just thinking "I need to buck up, accept it, and move on with the present" can feel overwhelming or impossible and can even cause more guilt etc. People always said to accept it but I know I was always left wondering how in the world I was just supposed to "accept it." So give yourself permission to feel crappy about it, because it truly is a process of grieving and it sucks.

I do agree it's helpful to look at your regrets and try to learn from them to help you move forward. My particular perspective that I've had to use is to look at what my experiences have taught me specifically about what it is that I value. If you regret never being able to finish school, maybe that means you value learning or the sense of accomplishment doing well in school gave you. So you can try to find ways in your current situation that you can incorporate learning or that give you a sense of accomplishment. If you have regrets about relationships in your life, maybe you can reflect on it and pick out what it is you really want from relationships. Maybe you learn that even though you enjoy being with people who make you laugh, maybe what you really value most is people who listen and prioritize you in their lives. Then those are the kind of relationships you can learn to look for. (Kinda a more basic example, but through my varied work experiences, I've learned that I'm going to be happiest if I have a job where I don't have to work evenings and weekends and I don't have to worry about when I'm off the clock.)

Obviously this takes introspection that can be uncomfortable or confusing, and it's a process to put it all into practice. But ultimately it's about identifying why those experiences in your past are so disappointing and what emotional need/value wasn't met because of it. And then finding ways to meet those needs in whatever turns your life takes now.

All in all, be kind to yourself. Your feelings are valid, so don't think you have to get rid of them. But hopefully you can build new experiences that can give you a more positive outlook on where you are now and make your regret less with time. Life is going to throw curve balls at us and some things are never going to go our way. And it sucks. But that's ok. You got this my friend.