Hi OP,
Your post is EXACTLY what my mother has been saying for years about my father. I have never known my parents happy together. My mum is living the exact same way as you talk about (without the autistic child). My dad has no friends and alienates hers, nobody ever comes over, etc. Ever since I was a kid, she's constantly told me how unhappy she is with the way my dad behaves (I suspect he might be on the spectrum, but that's another issue), but she won't do anything about it. She says she has no money to leave, that my dad won't give her any money to leave, and tbh I don't think she has the balls to go anyway.
I have told her time and time again that life is not a dress rehearsal, and I've used what I've learned on MN to tell her that she'd be entitled to half of anything he's got, so money shouldn't be an issue. But she still won't do anything. They're in their 60s/70s now and yet won't do anything to improve the situation while they still can.
I feel pretty well qualified to speak from the child's point of view. I'm not saying you complain to your kids about how you feel, but they most likely know or suspect. I've never lived through a divorce but I wonder if it's any less of a headfuck to see your parents tolerate each other and live a permanently miserable existence as a result. In my own case, I've been pretty messed up with the way they behave and then come bitching to me about the other. After a while you just want to bang their heads together, get them to make the break and find contentment separately.
I've promised myself I won't ever be like them - I tell my DH and DC every day that I love them, and I refuse to end up in the same situation as my parents have.
I do feel I should add here that my mum totally coloured my opinion of my dad for years. For years I thought he was a nasty piece of work, then I realised he and my mum just don't understand each other and have no way to communicate. She's not entirely wrong in what she says about him, but she was very wrong to influence my opinion. (A close relative says my dad actually adores my mum, and I think that's probably true, but he doesn't know how to show it, never mind say it.)
So apart from the fact that you deserve to be happy, maybe make the break so that your kids get to know their dad themselves and not through the lens of your unhappy marriage. Remember that your relationship may well influence theirs in future - kids often base their relationships on the model they've learned at home. As I say, I've never experienced divorce, but I wonder if kids benefit more from seeing two parents happy when apart than they do from living with two parents who can't stand to be around the other.
Sorry this turned into such a long post/rant. I do feel for you.