Nice to hear from you again, but sorry it's in response to some disappointments you've experienced.
You raise a lot of questions, which I'll try to respond to, not necessarily in order of presentation or importance (apologies in advance for any I might miss or answer incompletely).
On a practical level, I think looking for a better therapist match is an excellent idea, and likely one of the most critical actions you can engage in it at this moment in your life.
With regard to what you do next regarding school, you have many options, most of which maintain pathways to your future goals. You have acceptances to three highly-regarded major research universities (from what I understand), and goals that will probably require graduate studies. Attending one of these universities for your bachelor's degree would be as good of preparation for acceptance into a top-tier graduate program as you make it. You could also apply for transfer into a desired university some time before you have completed sophomore year-level credits. IOW, you don't need to be in an elite university this fall (especially as a member of the class of 2024, where most of the schools you listed--including the ones to which you were not accepted--have already decided that they will be predominantly or entirely online this coming school year), in order to achieve your goals.
I understand that one of your particular concerns is that even university will be insufficiently challenging academically. That would be a conversation to have (respectfully, of course) with your college advisor, including discussions regarding the level of, and how well you were performing in, your research and coursework prior to (and even after) a mental health crisis. It may be possible to explore connecting with a faculty member in the mathematics or applied mathematics departments to request an override into higher levels of math coursework than typically expected for freshman, perhaps supported by letters of reference from your past professors, or sample work from courses you have taken either for credit or even incompletely. They may be able to offer you placement testing, or course credit or placement by testing out. You may feel that the rupture in your educational path that occurred this spring (which you attribute to your reaction to admissions decisions) negates your other accomplishments in the eyes of others. Please remember that nearly every student on the planet experienced massive disruptions to their education this spring, so faculty members and university programs are likely to be somewhat more open to extenuating circumstances this admissions season.
With regard to your native and current cognitive ability, I would reassure you first, not to jump to conclusions that you have injured your capacity with your recent substance use. At the same time, I obviously cannot understate the risk to yourself and others involved in misuse of psychoactive substances. Further, please make sure your prescriber is fully aware of any other psychoactives (and preferably discontinue their use) prior to starting your antidepressants, as the risk of drug interactions is not one you want to run. As to your level of cognitive function, we have previously discussed the possibility of increases in formal IQ scores in persons with ASD, due to increasing testability. Certainly, that is a distinct possibility in your case. We have also discussed the greater value in actual performance than in predicted performance; your level of academic achievement clearly exceeds your predicted achievement based on very early (and likely low confidence) formal cognitive assessments. This is probably not worth additional anxiety.
Finally, circling back to an earlier thought, you may wish to consider where you will have the best support system (i.e., at UCLA, at UW, at NYU, in a CC, exploring your own interests while holding a job to meet basic life functions, focusing on your mental health, etc.) for optimal function in all aspects of your humanity. I don't know what supports you would have available to you in each of the options you have, of course; I would strongly encourage you to make assessing that part of your decision-making process.
Courage.
