AIBU to tell him to buy his own food

@Woodfiresareamazing2 described it perfectly: in his mind there is only his way or the wrong way.

I am self-diagnosed autistic (on the waiting list). Way back in my early twenties my then-partner accused me of always wanting everything my own way.
I said of course I don't, it is not about 'my' way, I just want everything done the right way, the best way.
He said "but you always just assume that the right way is your way".
That hit me like a bolt of lightning between the eyebrows.

My mind immediately thought "yes, everyone thinks their way is the right way."
I assumed I was correct and everyone else was wrong, and everyone else makes the same assumption. I even saw that there could be value in talking about other people's ideas, just in case they had thought of something that I had not considered.
But unless they argued and proved me wrong by pointing out the error in my logic, I was still right.

It took me a few more decades to realise that most people just don't want to bother to have that argument. They don't feel the same need to optimise every single thing in life to 'the right way'. That other people just don't care about optimisation, or don't even have the intelligence to realise there is such a thing, but they do take great exception to the feeling of me being bossy, controlling, or wanting to 'have my own way'.

You see how alien autistic thought is? It partly comes from having different core values and seeing the world differently.

When he 'just tells you how it is', treat that not as him being controlling, but as merely his conversational style: the opening line of a discussion, whereby you 'just tell him how it is' in return, and you argue it out in great detail, then finally agree.

If you don't have the stamina or energy for it, you will just need to assert your boundaries and hold firm, which may mean closing the joint account. If you are not 'in it together' with him ('it' being everything from a joint account, shared kitchen cupboards, and a willingness to keep on engaging in relating and discussing), you may find you end up living like housemates.

I think many NT people see disagreement or being told you are wrong, as rude- a sign that you don’t like or respect someone.

I think a lot of ND people see it as StandingDesk describes- an opening position, where they assume that they are correct and other people need to make a case otherwise if they want their way to be considered.

That leaves NT people needing to stand firm, cool and calm in a situation which feels like an attack.
Personally we made great progress as a couple when I stopped ‘looking him in the eye and challenging him’, and started instead ‘disagreeing then getting on with my day while not doing things his way’.

I used to turn myself inside out trying to accommodate, make partnership happen. Now I just do my own thing, often much to his surprise. He needs to make an effort to address things he is uncomfortable with now, rather than the onus always being on me to resolve or compromise.

There can be deeply rooted misunderstandings too. DH thought ‘sorry’ was what you said when you’d deliberately done something wrong- ‘been naughty’.
It took a while to show him that you say it when someone is hurt or disadvantaged by something, regardless of the intention or even the fault.
He’ll even say it occasionally now 🥳