Also always had health insurance so none of this has too do with that.
You said you've had no luck trying to get inpatient psych care by going through the ER, and you've done at least one failed intake interview for inpatient.
Getting good inpatient care is hard. And, like you've experienced - you won't get there through the ER.
So: if you can't do full private pay, and want to work within the health care system to get help - it sounds like you're at minimum going to need an advocate.
You might qualify as a vulnerable adult, and that would get you access to a social worker (caseworker), who could help you with communicating your needs. But you'll (probably) need to go through all the steps of obtaining a primary care doc, being referred to a psychiatrist/psychologist, possibly neuropsychologist, and then (finally) being referred to an appropriate inpatient or outpatient program.
Because, there are any number of things that could be leading to your outbursts...But I want to echo what Friday said, here:
Autism creates a baseline neurology that is difficult & complex to work with... in no small part because it’s such a HUGE spectrum...Add in things like trauma &/or other comorbid disorders? <low whistle> PTSD is relatively simple/straightforward. A lot of other disorders are fiendishly complex/complicated to work with.
You'll need to sort out your autism, and whether or not it's the main cause of your explosions. If it is, then no amount of cognitive therapy (like dialectical behavioral therapy, DBT - or cognitive behavioral therapy, CBT) is going to help. And if you try and do those things on your own, without any guidance from an in-person doctor or therapist - you'll potentially become even more upset and frustrated.
It's why I asked about money, because in the US, money cuts through the hoops. You'd just have to get to a good hospital (McLean, Mass General, John Hopkins, Mayo Clinic, UCLA, Stanford, Mennenger Clinic...).
Here's a few links for resources for adults with autism
autism speaks website, resources for adults
Dead Link Removed
UCLA Resnick Neuropsych center autism info
I'm not saying you're not also dealing with PTSD, it's possible you are - but it sounds like your diagnosis isn't going to be straightforward, and it could make a difference, to get it right.