You seem to have raised a good son.Hopefully he will mature soon even if a bit late on account of the ADHD.
When i was going through parenting stress I found it helpful to have hobby and community groups of my own outside the home, and when life was too busy to go out to play online games and attend online support groups and author fan groups. at first through usenet If you want ideas for groups i have dozens lol
I have a washing machine that also dries and wish i had it then. Sometimes really simple change made life better,. More pillows, a place to sort laundry, a repurposed box for shoes under the table at the entry. (an old frock pulled over the box makes it look OK) im not good with change so i got dh to help spot times it could help.
it was at times hard to even cope with anything at all so i had disposable knives and forks for crisis times and still use recycled paper plates a fair bit.
. One thing we always did (still do) was pay for cleaning with tidying. This was essential to survive. It can be hard to have the cleaner see the worst, but It is blessing to have them. Over the eyars i have seen that hiring a cleaner is a marriage saver for many people.
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Time alone can be tricky I formed a habit of waking before everyone else. My own mother often woke at midnight for a few hours (still does on her 80s)
My friend and i would arrange to bring our sons to each others houses and one of us would often go to sleep sitting in our chairs. it ended up her always coming to ours. . We still meet and sometimes sleep in our chairs and the grown up kids have their own meetups now. Could visitslike this be possible with your disabled family member.
I wore a book for years If my mind got overwhelmed i put my head into the book.. An aunty uses music that way,, My mum gets overwhelmed by music yet listened to documentaries and stories on radio and now on the net.. A sibling had the phone wired into his car handsfree for the many many times he was waiting for kids to get out of scouts etc.
For the worst year i chose self help positive books, Now i read whatever i like and i have a water resistant kindle i can even take to the shower. No, i got that wrong, the worst years were when I didnt read. For my aunty they were when she didnt music.
I know someone whose worst year was when they did not knit, they spin as well and the idea of all that work being relaxing makes me giggle for some reason.
ADHD meds mnay be hard to get in the UK , but if he is approved already perhaps he might decide to try different types but it will be up to him. One of our adult sons (30s) has adhd and has chosen not to have medications since he was in his teens.. He choses his own adventure, and it is alright.