Dear goodness, I could have written this! I can only really tell you our story and what we did and how there IS (touch everything wooden in sight) a potential happy ending.
DS is ASD, but very high functioning. However I think we had all persuaded ourselves he was higher functioning than he was. He started Uni last year, all seemed fine, was back for Xmas, all happy. Come end Feb, I had a funny feeling something was awry, went to visit him, after 24 hours it emerged he'd dropped out academically in the October after getting behind with an essay and just hid, ostrich-like (YTAF did the Uni not contact me/him??) and then socially too, as was embarrassed in front of his friends, so just sat in his room, went nocturnal, survived on Nutella (found 24 jars in his room)...I whisked him home.
He saw the GP, was put on ADs (even if he hadn't been before, 4 months of isolation would send anyone potty) and referred to the mental health services. I had to fight for all this to happen ASAP. Screaming matches with receptionists etc. They put him on a course of CBT and he also saw a private counsellor about mindfulness (he genuinely enjoyed this).
We had 4 pretty shitty months, when he just sat on his PC, that's if he was up at all. DP went into work mode ie problem/solution and kept coming up with various star charts eg if you go swimming every day/get a job we'll go to Nandos/sushi...Didn't work.
All that did was time, understanding, lots of heart to hearts with me, the ADs kicking in, and then some gentle planning for the future.
We visited another university and had meetings with their MH people and got DS registered disabled so he now has weekly meetings with a mentor to keep him on track (he started there last month). He also used some of an inheritance to go travelling, and I disagree with some of the posters above - it gave him something to focus on, plan for and get excited about. He managed really well - re-learning independence, responsibility etc. He checked in with a relative of mine who lives there halfway through so that gave me some peace of mind, and I insisted on daily texts.
The single best thing though was, like you, I got him on a short course with one of the tutors at our local uni on a vaguely connected subject that he's always been interested in. It got him out of bed twice a week, and started to rebuild his self esteem and worth (and got DP off his back).
With your DH...I dunno. Maybe you two could go out for dinner and in a non confrontational, neutral setting, rather than having harsh words about it all when you're freshly exasperated at everyone's laziness, talk instead about how it makes you feel, value, respect, lack of etc...and then also agree a joint plan for DS. But crucially, DS himself then needs to be part of and sign up to that plan.
Hope this all makes sense - do PM me if you want to talk more as it's eerily similar and I suspect you might be feeling like I did - heartbroken, failure as a Mum etc. It DID get better x