I own two small businesses, and one of the best pieces of wisdom I ever got from another business person was that people almost never have business problems. They have personal problems that manifest in their business. I've seen the truth of that statement in my experiences with people over and over again.

Ultimately, he will never be successful unless he sorts himself out personally. If I was you, I would use your management of the money as a positive motivator. Like, "Hey! I'm so excited about your business; I really want to help manage the money for it!"

And then you can get him to create a solid business plan, research the right loans/investors, do some market proof of concept work and research, etc... all as part of helping you better financially plan for the business.

That all being said, I really think this business situation is a symptom of much bigger issues that really need to be addressed. Things like this will keep coming up.