&gt;I realize that his inability to handle money is largely my fault

Are you his mother?


&gt;he is a high functioning alcoholic

Yet.


&gt;If I try to say anything about the plan or ask any questions about his business plan he takes it as me not being supportive. The only thing he wants to hear from me is how awesome this idea is and how successful he will be


Inability to defend his ideas is an indicator of failure. But, his failure can be an eye opening for him, so let him.

Here is what you do:

1. Set a rule that absolutely no family money can go towards his business. His business is 100% his responsibility, you will not do anything for it in any way.

2. Give him three months to find investment money AND start bringing home a salary not less than he was earning before. If he fails to find an investment in three months he has to get back to work immediately.

3. If he fails with his business or fails to find an investment, he has to stop consuming alcohol and go to AA or any other program.

4. Have him agree to these rules when he is sober, draft a contract and you both sign it at notary office.

5. Tell him if he fails and blames you for not being supportive, you will divorce him.