Odd story: fellow I know, good friend, never really got out and lived his life.
His mother and grandmother are quite mad, more or less. Granma was a super-neat-control-freak-obsessive, who lived on into her mid 90’s (she passed away just two years ago). His mother became, under her domineering influence, the precise opposite and lives in surrounded by filth. Things worked well… except that Granma lost her strength and couldn’t do anything long, long before she died.
Thus, his mother lived in this terrible mess, largely incapable of taking care of herself, and sort of throwing minor fits of passive-aggressiveness around. These quite often take the form of creating messes, or dumping piles of crap where they definitely don’t belong. Her place is a huge pile of dirty laundy everywhere and clean laundry she dumps atop other, dirty stuff.
My friend never really left. The two females were so nuts he pretty took care fo tyhem, as they were incapable of yardwork and anything practical, though his mother often wanted plants in places where they’d simply die, or made a “minor” request which calls for a huge amount of work and then throws a passive aggressive fit if it’s not done.
Guy never got married (is getting towards 50 now), though he lived away from home for a long while. Lives his the mother now, taking care of her. Probably will forever. Very sad.
Be his external outlet. Get him out of his house and into the real world.
Heck, I’m a very quiet and private person and there are a great many places that I just don’t go on my own, but when I was married/attached, or when I have friends who are willing to go, I go to a lot of different places.
So take him to those places. Start slow, just going out for lunch, out for a beer. Hang out, form a relationship. You don’t even have to explain it and I’d recommend that you don’t, but get him used to the idea of going out and about with you to do things. Once he’s comfortable, and if you’re comfortable with the friendship, then start going other places. Go to the movies once a month or so. “Hey, there’s this cool show of (fill in the blanks) art at the museum, wanna go?” (I dragged my ex to the Mpls Institute of Arts when there was a big show of Egyptian artifacts. Dunno if either of us would have gone on our own.)
At the start, you can let him vent a little, and might even want to encourage it just to get to open up. But after a while, that will get old and you might end up having to tell him that while you appreciate his problems, the point of the outings is to leave those problems behind and have fun.
If you really want to help him, this is one path. He’s probably never had anyone to help him walk out that door into the wider world. It might open his eyes.
That is my family story except replace your friend with my sister. There’s nothing you can do to for him except be his friend and when his mom dies help him clean up the mess.
Scary thing is though my sister turned into my mom and still does nothing about the mess even after my mom died.
I would swear this is a family member talking about my aunt, except my grandmother passed away a few years ago so now she’s only has my grandfather to care for until he passes.