I'm bumping this for you because I have a son who has asd, high functioning, with co-morbid OCD.
When you say heis possibly autistic, I'm presuming he doesn't have a diagnosis. He is not alone. Many many adults have referred themselves for diagnosis, as all the current media enlightenment and better diagnosing had brought to light how very common as condition this is.
You may have done these things already....
Contact your gp and explain the situation candidly. Your son would need to see the doctor but seriously, depression and suicide among young men, is so prevalent, I'd really encourage this as a first port of call.
The National Autistic Society can be helpful and have really sympathetic people on their information and help line. If you haven't, get in touch, they may be able to guide you. They may know of adult groups in your area or social outlets.
This may not suit your son but, would he consider some local voluntary work? Contact the Direct.gov or any 'volunteering' websites. That way, he could ease in gently. He need not to commit to too much at first and, there's no pressure, it being voluntary. It might give him some confidence, he might add to existing skills, he'd meet people, it'd get him out of the house for as long or as little as he can cope with and work may develope from that. Just a thought.
Let us know how he gets on, will you?