I am a diagnosed aspie and I've never felt a few moments of genuine ease in my 20s. I want the continous self-criticism to stop, the panic attacks, the revision of nearly every individual thought to ensure its socially appropriate, etc to get on with my life and end my financial crisis.
Short answer: Time, experience and luck.
Long answer: I know exactly how you feel and I could have wrote this when I was in my late 20s. I have never been diagnosed but easily can check all the boxes so I am almost certainly on the spectrum somewhere. As long as I can remember I was always considered one of the odd kids. I was/am very quiet, not because I want to be but because I am afraid that I will say something wrong and people would think less of me. Constantly thinking everything out to almost paralysis and almost always settling on the worst possible outcome so I would abandon the idea.
To this day I still relive events from as far back as when I was a 4 year old and beat myself up for doing the wrong thing. Once I had a career, I found myself in situations that I could see what I needed to do and could easily tell someone the proper thing in an instant but time after time I retreated inside my own head where I would tell myself everything would go wrong and I wouldn't do it. Finally one of those times where all I had to do was simply go introduce myself to one person led to me fleeing the scene and having a full blown panic attack, I cannot remember how I got home. Later that day I scheduled an appointment with my Dr and he prescribed some anti-anxiety meds, citalopram I think.
Unlike some on here I did not notice a night and day difference, I still had the same thoughts but it was more like I had a single drink in me. I was a little looser but all the same problems still existed, I did not have any more panic attacks though. I was on some kind of med for four years or so and people are completely right about not being able to just stop whenever you want, stopping does not go well unless you wean yourself down to an almost ineffective dose. I have seen some research that says some of these meds have some kind of permanent influence and that may be the case because I did not go all the way back to the way I was before I started taking them.
I have been off any meds for about six years now. I am also a different person than I was then too. I still overthink way too much stuff but I have been able to convince myself not to do that as much. I am still pretty quiet but I will speak it is just part of my personality to listen for all the information and not vomiting out ill informed crap. And I have not felt the need to flee a situation in a very long time. Did the meds help some of this? Possibly. But I believe the most important thing has been punching my brain in the face and just doing it, it is terrifying at first Over time I was able to add positive results into my thought process that used to be all negative. The more times I succeeded in not being an idiot, it's going to happen but not nearly as much as you think it will, the more I stopped thinking that was what would always happen.
So over time I gained enough experience that the self doubt was reduced and I gained confidence. All those other times that stuff went right but I really didn't do anything I call luck, and it has happened enough that I actually feel pretty lucky now and that helps as well.
Just look at my posting history here. I lurked daily from 2006 to 2011, created an account because I thought I had something to say but talked myself out of it and then finally said something about 2 years later. At some point early on I even made a post in L&R asking for help being more social. But over time I posted more and more because I am not scaring myself into inaction like I used to but I do still rewrite these about half a dozen times before submitting.
One problem I don't have is love. Once upon a time I was 20, sitting in a car playing GTA while fifty other people talked in the parking lot on a Saturday night. A 15 year old girl said she kinda liked me to some of my friends and so they did what friends do and locked her in the car with me. Now she was pretty self defeating as well but managed to choke out that she liked me and I was too afraid to say anything other than OK. 16 years later we are still together and have three kids. Again I was incredibly lucky and we work almost perfectly together, so I cannot much help that part of your problem.
I am not saying I am cured and I still battle with it every day to some degree. I don't have any real life friends anymore, I stay at home more than I would like, and I still have to force my head into doing things. But I do believe that it will get even better with more time.