How do I properly grieve? I realized I never got over anything ever, & I want to move on in life. I want to feel it, and let it go, but i dont know how.

As the year wraps up, i am cleaning house. I realized that there are things I thought I got over, but never did. Sneaky emotions rise up, and when i finally noticed them, I realized the thing they're connected to is something I never acknowledged.

Real example: I am 27. I fucked up so bad in college. I was a straight A student in high school, got too college and it was the worst time of my life. I had no friends, no meaningful connections. I graduated with a 2.3 GPA in biochemistry. I wanted to be a doctor to prove I was smart, but never gave thought to what I actually wanted to do. I look at people online reminiscing about college, i see my younger sibling in college, and watching them actually lives makes me happy for them, but invokes a pain in me. I was sick, depressed, miserable, and stupid then. I wish so badly I could go back and redo it. I'll never have the kind of fun "carefree" life again that you're supposed to experience in college. Recently I saw someone online that was being praised by her friends. Not a single person had a bad thing to say about her. I was instantly jealous, and felt this deep ache of regret and sadness, that she had made memories and meaningful connections. What hurts the most is knowing it was all my fault, no one to blame but myself.

I don't know why i care so much. But i never grieved what i missed out on. I recognize I can be whoever I want now, and make those memories and connections, but i dont know how to grieve the past and let it go. I do know that the sneaky feeling of jealousy, regret, sadness comes up in my chest, gut, and upper back, but I dont know how too let it go.

Its not just college. There are a few other areas of life I want to get over. But they are in the past. 1 thing is ongoing but yeah. How do I recognize something, actually feel/grieve it, and let it go?