Hi Gail,
My heart goes out to you and your son. This is not an easy situation for any of you, but I agree that something needs to be done. At 33, your son needs to learn to be independent. You don't mention whether he has been diagnosed with more than ADHD, but it sounds like at the very least, he might be depressed.
Since he's lived this long being dependent on you, it will be very very difficult to get him on his own two feet and I would highly recommend that you consult with a therapist/counselor who can guide you. That is the very first step.
Then, be confident and strong in the plan that you work out with the therapist. Make sure your spouse is on board and willing to support your efforts.
Your son may need to know that he will get support for a short, specific amount of time and then he's on his own. You can give him names of agencies that can help him. You can insist on his getting help if he is to get temporary support from you- therapy, meds if prescribed, etc. As long as you continue to support him, you are entitled to make the ground rules. Your goal really needs to be to get him the resources he needs to begin living independently. One agency would include the Dept. of Vocational Rehab, where he can get assessed for vocational skills and be referred to vocational training and placement.
This is a huge step on your part and I can't stress enough the need for you to get help with all of this.
Good luck!
Terry