capewrath
Re tips on face washing/dish washing:
Use facial wipes rather than soap/water, or cream cleanser or wet cotton pads to wipe over face.
Buy a dishwasher! Or suggest ruber gloves, and running the tap hot and washing each item individually under it. Scourers/brushes preferable to squishy cloths.
I have asd and haven't put my hands in dishwater for over a decade- I'd feel like vomiting/have a meltdown. Water on my face is similarly repulsive- I only have baths not showers and avoid swimming. The world is a sensory minefield for me.
OP- I can see both sides of your situation. I'm a similar age to your DS and have similar issues. I am high functioning in that I have a DP, DCs and a career but I am very dependent on DP for personal hygiene etc. eg I'd go a month without realising I'd not had a bath so once a week DP will run one for me. I'm sensitive to the temperature change so he'll put the heating on, close the windows, warm the towels etc. DP does my laundry too as if I didn't have a particular reason to 'dress well' eg work/social event I'd sleep in my clothes, wear them stained for days etc. I hate the sensation of dressing/undressing. I'm also really particular about fabrics/fit. No one could buy clothes/shoes for me.
Re: toothbrushing, again I'm similar. I hate the taste of toothpaste and the sensation of the brush and most of all any that dribbles out around my mouth. It's a huge chore for me so I do avoid it. I probably only brush 3/4 times a week. But I have managed to keep my teeth decent by finding ways to keep them clean that I find more tolerable. (Partly this is to avoid the dentist) eg I floss 2+ times a day. I avoid sugar in my diet. I don't drink coffee. I drink liquids with a straw. I use the DIY dental tools you can get from the chemist to scrape plaque off my teeth after eating/drinking. Maybe some of these ideas could help your DS?
I also know what it's like to have a DS with asd. Mine is a teen. He is high functioning, undiagnosed. I don't doubt that he'll have a 'normal on the outside' life. But things like taking him to a cafe we gave up on years ago. He will never say he loves me or ever get me a birthday/Xmas/Mother's Day card. His teeth & clothing habits are similar to mine/your DS. My attitude is 'don't sweat the small stuff'.
He too only wants to talk about himself/his special interests. Even if someone else hurts themselves he won't show any empathy. We don't really talk very much at all, even though we live under the same roof we are like passing ships. He doesn't even say hello when he comes home. But I've just accepted this as the way things are. Like you I have another DC who I can have a 'normal' relationship with and I'm very grateful for that.
What I would suggest is that you find out about any local support groups for you (try nas/facebook) and adult asd groups for DS. I think he needs to find someone else to talk at/ share special interests with as he seems very emotionally reliant on you.
If there aren't any then have a think about setting these up yourself. It could have long term benefits if you can make a success of it. There will be others in your/DS's situation, you just need to find a way of contacting them. I think you would both benefit greatly from it.