I don't want to be like this anymore

I am just caught in a fucking loop and can't get out. Stuck in the same shitty city for 12 year, I am 31 now. Stuck in past situations where I could have just made up my mind a bit more, where I could have just been honest to myself or others about the issues I have and everything could have been better. I hate my mind, I had so many possibilities, a tall, good looking (I did not always see it like that), genuinely smart (never trusted in myself) and funny guy (that I always knew is true) and I fucked my life up so badly. Got in a bad relationship, got co-dependent, was too awkward to make or maintain true friendships, only thing in my life that brought me joy or distracted me from being miserable was sex.

All I do now is look back and hate myself for so royally messed up my 20s. Not by making mistakes that will one day be experiences, but by doing nothing and being stuck. I hate myself, I can't have a good time because I am mostly alone in my city at and lost touch with all my other friends. If I have a good time, my mind punishes me and makes me remember and regret all the good times I did not have. Recently, it even made sure that the best thing I ever had, a fantastic new girlfriend I found by some miracle, is gone for good simply through making me ashamed and sad by seeing her and my life in comparison.

I hate my mind, I hate myself and I think about dying so often. I won't do it, I genuinely saw myself at the very worst, as in, I can't imagine ever feeling worse and wanting to die more. I have hit myself or even banged my head against the wall. I have taken a knife, held it against myself and yelled that I should just do it, but I will not.

I know I listed some stuff about myself that some people in here that will make people say that I don't have anything to complain about. I listed many positives about myself and I did not even mention that I am in great physical shape and health and even have enough money to be unemployed for a considerable amount of time. I am sorry for complaining even many people have it objectively worse. But my mind is just punishing me all the time. I really want to be better. I see a therapist, I have told some people about having issues. I don't want to be like this, I really don't. but I have been this guy for as long as I remember and don't think I have the capacity to change.