I agree with ShinySparkly.
I have 3 dc, all have ADHD and two have ASD. They are still expected to behave reasonably and learn that compromise is essential when people live together. It does them no favours to be pandered to if they 'kick off/meltdown'. When they are out in the world they will need to learn to negotiate and compromise, and abusive behaviour is still abusive, whether it's caused by disability or not!
Eldest dc is 21 and her bf stays over occasionally when she's home from uni, but dc (12), who she shares with when home (very small house!), kips down on our bedroom floor when her bf stays over. Dc (12) very happy to do this as loves to sleep in a 'nest' on our floor and views it as a bit of a treat 😁!
"I'm sorry but he's 16. Autistic or not, that's old enough to understand and accept that sometimes he'll be told no for the simple reason that someone else's opinion trumps his. This is one of those situations.
He needs to learn that 3 days of WW3 because he can't get his own way or an explanation that he agrees with for why he can't get his own way, is entirely inappropriate. If he doesn't learn this, he's never going to have a long term successful relationship, because his behaviour is going to amount to domestic abuse every time he can't get his own way or disagrees with his partner.
So all he'll have is a constant string of people who leave him. People who'll have their own lives messed up by him. You're not doing him or his future partners any favours by pandering to this desire for an explanation. He simply needs to learn that he can't always have what he wants, that exploding in a rage (or whatever form his meltdowns take) isn't ok and he needs to find ways to cope with whatever he's feeling.
A sulky/angry person that people have to tiptoe round and cave in to their requests in order to avoid drama or justify their no with an explanation of why, is still being abusive even when there's a medical issue behind it".