I have a 30 year old son with ASD who lived at home until he was about 24. He moved out because, well, he wanted to and things at home were a bit tense due to his needs and moods.
It has been an interesting ride. On paper he has the skills to live independently but really, he lacks the motivation to carry these out to anything beyond survival/ existence. He had a twice weekly support worker pre pandemic but that stopped abruptly in March 2020 and I stepped in to help him with cleaning and shopping and so on. He will do housework if I'm there to supervise/ buddy him but otherwise...
He is very lonely. He doesn't really see anybody apart from me, and does not work. He has hobbies and interests which keep him occupied but I do feel bad for him being on his own so much. I don't think I could live with him for again, his needs for his environment are quite specific and we clashed quite a bit. I do feel for you, it's so hard realising that you are going to be needed quite intensely for life. Sometimes it gets me down that I can't - I don't know - emigrate to New Zealand or even just move cities for better job prospects.
In an ideal world, if I won the pools I'd buy a house for me and DP with a cottage in the grounds for DS so he'd be independent but close by. But that's not going to happen, realistically.
Does he have any involvement from your local social services team, or Autism Service? DS has access to a social worker and could get a support worker if he wanted (finding the right person is a whole other story, mind) - it might be worth exploring this if you haven't already. Also check out getting a carer's assessment for yourself. It might be weird to think of yourself as carer, rather than a Mum (it took me a while) but again, different local authorities have different provisions for carers which might help.
In the meantime, promoting independence is never a bad thing, even if it takes many reminder lists and active WhatsApp chats (this is how we manage). I also have a couple of trusted friends who will check in on DS if I'm on holiday, and who he knows he can call.
Stay strong, OP, and look after yourself, as well, getting support for you is crucial too.