For my Master's my research was on social welfare policy dysfunction. Specifically, I looked at disabled populations and barriers for them in higher education. When I went on working towards a PhD one of the requirements was that I have work in two additional fields. One of those was comparative governments. (The other was fiscal policy - gaaaak, retch!) So I looked at the same social policy area, but in the UK and (if memory serves) Germany & Scandinavia on a broader scope than just higher education. It's been a lot of years since I was behind the typewriter tapping away on all that, but if things hold as they were then, and from what I've seen in recent years, my general impression is that you are better off in the USA than in the UK, by a long-shot, as a person on the spectrum. Not sure I'd say that about the Scandinavian countries or Germany - IF you were a native of one of them. But I haven't spent a lot of effort looking at those in a long time.
You didn't ask for this advice, but I'm going to offer it anyway. What you do with it is, of course, entirely up to you:
If you're to be married, I think I'd suggest your partner try to live in the USA with you for at least the first several years of your marriage. Those are the times when you are having to become adjusted to being married - and it is an adjustment. Once all the flowers and the honeymoon fade there can be some hard interpersonal work involved. Being on the spectrum can make that... let us say "somewhat challenging"... depending on where you are on it and how understanding your spouse is. (Seriously, the last thing you want to do is end up divorced in a foreign country without a support system.) Once you've got a really serious grounding with each other after several years, then you might want to look at living overseas - if you still both want to do it.
And, as a corollary, the UK economy is going to have some very, very rough years for some time to come. The government has borrowed heavily to keep the economy afloat during Covid and post-Brexit, and they are still borrowing heavily. The piper will have to be paid someday, as the saying goes. It's a pretty good bet that the folks at the top of the economic pile are not going to be hurting much in that process. Everyone else is going to feel the pinch, and those at the bottom will probably find it more of a gut punch. (Example - The government won't windfall-profit tax the energy sector, where stockholders are earning hand-over-fist while home energy bills shoot into the stratosphere. But they'll propose cuts to social welfare programs to "balance the budget". Pretty amazing, but not very surprising.) One of the first things I expect they will cut will be funding that is directed towards helping persons with special needs. If you rely on their social net, you could find it doesn't help much. If it even functionally remains, in a few years.
Another thing to check, and I simply do not remember about qualifying (if I ever actually knew at all) - if you go overseas, does your SSI or SSDI go with you, or do you have to be a resident in the USA to collect those payments? In fact, I'm pretty sure SSI can't be paid to overseas residents. SSDI might be case-by-case, but I think it may be possible if you're already on it before you leave the country. (?) You will definitely want to know the realities before you do your planning if you hope to depend on USA disability payments of any variety while living abroad.
Good luck, whatever you choose to do.