Hi OP
I think you're brave for coming back , but far more pertinently brave to face up to the fact that your home is not a healthy one for your son at the moment.
I'm going to say something harsh.
I feel strongly and instinctively that you have a substance problem too. You might dismiss that as the hysterical pearl-clutching words of a middle class Mumsnetter who thinks smoking a joint or getting rat arsed sometimes is shocking and a sign of addiction (you would be far off the mark!).
You compare yourself favourably with your dh and other 'much worse' smokers, drinkers, drug takers and think you're ok. But deep down you know.
Your son wasn't at a family members house when you were shit faced on your last thread and you hadn't gone out. It wasn't 'rare' but in your mind it was because you probably struggle with days off, days on, different ways of managing it and it felt rare at the time.
My best guess is you were drinking and puffing with your husband as he/you had decided it was ok to have a blow out as you had both been 'good' and he was 'recovering'.
I think this is one of the main reasons why you can't or don't know how to deal with dh who has a worse problem.
I think his family see the both of you as co-dependant substance abusers and they despair.
Many of us on this thread know about addiction whether it's a family member, themselves, whether it's heroin or cigarettes. We know very well the minimising and denial. I myself do.