I can relate, sort of, but I do it a little differently I think.
Have you tried to figure out what thoughts and feelings you have before quitting or leaving? And what thoughts and feelings you have when you quit or leave?
I think it could help you to talk to a therapist about it.
I often quit or leave things or people, when I start to feel that it won't go anywhere, that it will end no matter what, so I might as well end it myself instead of dragging it out.
Like, if I'm seeing a person, a friend, and I don't feel like we are hitting it off completely, I'm hoping that we'll become closer, that I will eventually be able to feel at ease around said person... But it keeps being an attempt of a friendship, rather than a real friendship. And at some point I will stop texting or stop making attempts to make plans with the person, and in a few cases I have even told them "hey, I don't think this is gonna work out".
Many friendships ended because I needed more out of the friendships... And I haven't fiugured out if I should just expect less from friendships... Maybe I should. But as a minimum, I want to feel at ease around someone I'm friends with, and not feel awkward.
When it comes to anything that has to do with career or hobbies or my skills, or usually stop it at some point. I stopped drawing and painting. Well I might begin again, but I used to do it a lot more and I haven't done any drawing or painting in a long time. I stopped horseback riding. The only thing I haven't stopped is playing music, but I have long periods of time when I don't play at all.
I guess I feel that everything I touch is pointless, and I lose my drive. I lose the belief that it will go anywhere. I really don't have any belief that anything i do will matter or will make me succesful in anyway.