Sal, i just read the whole thread, so sad to discover you got the Double Lie. That first lie of omission for three years, and then the attempt by him to minimise what he did by lying again and seeking to blame you for what happened. And here he is, STILL trying to turn it round on you and make you responsible for his self-inflicted misery.
Well, hear this and repeat: this is NOT your fault. None of it. And anything he does now, or in the future, NOT your responsibility. How DARE he put more sadness and stress on you, after all the crap he put you through when you had your DC's diagnosis, years of behaving badly, then the revelation of the affair, then the botched attempt to reconcile leading to the full revelation and separation.
You are a strong and capable person, a fantastic mum with a huge heart. That much is very clear. I know this must be an incredibly hard thing go cope with, but you will get through it.
Honestly the shame for his errors and the failure of this relationship is NOT yours to carry. So hold your head high. Don't be afraid to let people find out your business - tell them loud and clear that while you were coping with your DC's disability, your DH was drinking and taking drugs and shagging around. And you've decided you can't waste any more of your life with him, even though you loved him it is time to move on. People will have huge sympathy for you and I'm sure you'll find a well of support out there in your community. So many women have lived through a similar nightmare, the details vary but it's a sadly familiar tale that really only reflects badly on HIM.
You don't have to feel ashamed for being in love with him. That makes you a good person, an optimistic person, the kind of person who most of us aspire to be.
Thinking of you.