My partner (probably shortly to be ex partner) is autistic and exactly like this.
My grown son is also autistic, as is my sister, dad and uncle and none of them do this.
My relationship with my DP was amazing in so many ways, best friends, laughter, love: and I'm very easygoing so was able to cope with the rigidity, but then it started to damage me and us.
Over time three things materialised.
Firstly, I couldn't get him to do perfectly normal, rock bottom things without a complete ordeal that would be just like you say - literally years to get something simple. I'm not needy, the stuff I'd ask would be basic and essential to my wellbeing or ours and he would say he would do it and then not do it. My life became an ordeal. To literally get the most basic commitments kept, I'd have to fight like mad and then getting it never felt good after all that anyway.
Secondly, he wasn't able to follow 'rules' or parameters for basic healthy life together. For example skills like listening without changing the subject to himself. Empathy of how I might feel if he did something hurtful. Learning from mistakes and not repeating them. Understanding extreme selfishness can't work. Making healthy choices that gave positive results. He just couldn't do those things. So he'd doggedly repeat maladaptive behavior over and over.
Thirdly, he'd lack and reasonable route out of conflict and prevent me from getting out of it either unless I just accepted his (wrong) method of smoothing things over. Just as an example here of what this means:
He might say something really, really hurtful that he refused to accept was hurtful. Like a great example is that he used to repeatedly say his life was better with his ex. Now, my partner doesn't even like his ex, but he liked his life. They lived overseas and had a pool etc. So he would go om and on and on (typical autistic to get stuck in loops) about how great his life was when he was wealthier with nice weather and a pool.
By almost anyones standards this is immensely hurtful and I'd ask him to stop. But three years later he'd still say it 3 or 4 times a week - sometimes for hours on end. Long rants. Initially I asked him nicely to stop and explained why it was very hurtful, and he'd apologise and say he liked ME better but just his HOUSE and everything else better before. I'd say, that's fine, but still please don't say this anymore as it makes me feel like you're being negative about our life and comparing it unfavourably. He'd apologise very heartfelt and within an hour be doing it again.
It's compulsive, destructive behaviour that led to me getting upset, depressed, angry, withdrawing from him and having lots of endless rows which were caused every time by him saying something he'd been clearly told and shown was not OK. He couldn't stop. Then he'd say "you're always criticising me!" or "I love you but these rows have to stop!". Which is basically DARVO and it made me in the end very unhappy.
We really loved each other and this was ruining both our lives and the relationship but he simply couldn't stop. I tried everything. We'd write a short list of rules to follow to stop the rows and he'd be crying and swear he'd do it - and within 24 hours he'd be breaking the rules and then angry and defensive at being 'criticised'.
There isn't any way he can change. It's not possible for him. I've exhausted myself. He's unable to get out of loops, he has really bad empathy, he can't follow rules, he can't accept reasonable consequences and he can't respect boundaries. Its impossible for him.
None of the autistic people in my family have this, but I believe my partner does because he has Co existing issues due to abuse in childhood. He never learned the things needed to love and be loved. He has certain characteristics developed for survival and he can't change them (or won't).
As I've said all the above, let me also say this. My partner worships the ground I walk on. In many other ways he'd do anything for me. He does so many wonderful things. We have so many great things between us. I've no question I'm the person he loves most on earth, but he's unable to co-exist with compromise and boundaries and his behaviour has made our lovely relationship painful and hard.
I'm unable to get often basic needs met.
I'm sorry this isn't answering your questions, but after many years of those I want from positive and enthusiastic to feeling like our of us would need a lobotomy.
I've left him a few weeks ago and he's completely and utterly devastated and has started doing literally everything I was asking for that he was making an ordeal before.
I can't go back, because if I do, he will definitely revert. He can't stop. Not unless I leave him, which is no way to live.
I love him enormously, but I can't live with him.