That's another thing that I feel guilty about. I should have recognised the alcoholism much earlier than I did.
No. He should have recognised his alcoholism much earlier than he has.
His alcoholism is not your problem to fix. Not least because you can't fix it. Even if you were a trained alcohol abuse specialist you still wouldn't be able to fix his alcoholism until and unless he decides he wants help.
He lost his driving license, he lost his job, he lost his family a home, and he eventually lost his wife and kids. All through drink. No-one held him down and poured the booze down his throat. He chose to. These are the inevitable consequences of his choices.
This is what happens when you choose to piss your life away. Little by little, bit by bit, you lose things. You lose jobs and people and relationships.
One day the amount that he his drinking has lost may make him wake up and realise that, no matter what, he cannot face losing any more and he'll make positive steps to address his drinking.
At the same time if he wants to do something about where he lives then he can. He's choosing not to. The more you try to deal with his life for him the more you will be sucked back into worrying about him all the time.
A useful reminder is to think "Is this something that he could, and should, be dealing with by himself?" Talking to environmental health is just such a thing. Finding somewhere else to live is another. Fighting his case with the GP is a third. He's a grown-up. He might want you to act like his mother but for you to take on that role would be doing him, and you, a disservice.
His life will carry on being a slow-motion car-crash whether you spectate or not. You've got enough on your plate as it is. Leave him to it.