Lea, welcome to the site. My son is 27. He does have diagnosed mental illness, a mood disorder.
I would guess that your son too may have issues, whether diagnosed or not. But that does not mean he does not need to take responsibility for his own life.
I am glad you found us. The article on detachment that Kalahou recommends is helpful. The member scentofcedar has a link at the bottom of her posts about how to talk to your adult children. You can do a search for her posts (upper right is search) and you will find it.
Here it is:
http://drkathleenmccoy.blogspot.com/2012/06/helping-adult-children-through-rough.html
Many of us have found that we have not helped our children by "helping them" and we have made ourselves miserable too.
It is time for your son to live under his own steam. He will grow this way and you will feel good as you see him responding successfully to the challenges he faces. You will find your own integrity too, as you insist your son find his.
I am so glad you found us. You are not alone in any of it. It is slow this time of night, especially on the weekends. Tomorrow morning others will check in.
Keep posting. It really really helps. Posting on your own thread and threads of others.
Take care.
COPA