Ops dh (and op to a certain extent) with the kindest will in the world this avoidance of confrontation is utterly self defeating! It's not solving ANYTHING it's just burying your head in the sand!
Nobody LIKES confrontation but sometimes it is NECESSARY and this IS one of those times!
Your failure to deal with him and the issues he is causing is causing far more harm to FOUR people THREE of whom are blameless in all this than a confrontation could possibly do.
You are doing him NO favours pandering to him, bailing him out and shying away from DEALING with this!
He is behaving like an overgrown toddler, lengthy reasoning discussions WILL NOT WORK.
Clear and consistent boundaries will be much better
I would suggest:
NO staying at yours AT ALL until he gets a job!
Even when he does no staying more than 2 nights in a row
NO drugs in the house!
NO lock on his bedroom door - it may be "his" room but it's YOUR house and he blatantly cannot be trusted.
NO more bailing him out - at the very very LEAST no cash! You are funding his drug use! Do you want to be buying his drugs? Contributing to his worsening health and possible death?
NO entering into discussions about your rules, him "diagnosing" you (such a deflecting pile of bullshit by the way) he likes it or lumps it!
NO aggressive or manipulative behaviour on visits or he is OUT!
I know it's hard, believe me, I'm from a family full of addicts I've seen this play out and the way you're doing it? NEVER ends well. I'm pulling NO punches, sorry if this is shocking and seems harsh but ime its true - it can result in the death of the addict.
But clear rules has a CHANCE of improving things, at the very least for the 3 of you still living in your house.
PLEASE seek help and advice from whatever local family of addicts support services you have locally. They will have seen this and worse many many times.
I have lost too many people to addiction, it's a selfish bastard of a condition and it needs starved of all oxygen!
PLEASE don't end up coming on here in the next 5 years having lost your boy altogether. NOBODY wants that and that is as far as I can see where this is headed.