It looks to me like you are thinking only in black and white terms. To you, things are either this way or that way. You say you are either intelligent or not. Books have something to tell you or don’t. Psychology is useless but maybe it isn’t. You want a social life but find it boring. Either do something big or why bother. And on it goes.
To me, a diagnosis isn’t as important as what you are doing with your life. On the basis of your letter, I’d say you are too ambitious. You have big ideas but they are so big that it seems impossible to achieve them. Rather than try and fail, you give up. That saves your self-esteem but it also leaves you feeling hopeless.
The reality is that almost everything in life (except maybe death) is on a spectrum. For some reason you can’t deal with that fact so you opt out. I don’t know why you won’t talk to an “expert”. A few sessions with a counselor might help you sort out why you are so easily discouraged and what you can do about it.
For the record: I do think you are intelligent and that you are asking big philosophical questions. I do understand that it is easy to feel small in such a big universe. Part of being human is to grapple with that and to do what we can to make a difference anyway.
I wish you well.