Yes this is the type of thing that people divorce over. Money is one of the 3 marriage killers.
If you both have been having trouble getting and / or keeping work he probably see's the being his own boss thing as a source of security. He also is likely to take any criticism of the business as a "I don't think you can do it" kind of statement and that's just going to make him defensive and stubborn.
It's a scary boat to be in. Business loan, mortgage and having to actually get the business off the ground. Rather than be pessimistic about this, maybe do what you can to ensure it will work for him. (where in aus are you by the way?) Vista Print do very cheap business cards and flyers and you can always just go drop them in letter boxes. Local papers often do very cheap advertising too. if you are with the company I am assuming (Jims) they also are very good for general advertising.
I have a friend that was a qualified chef bringing home around $1500 a week. He got jack of the hours and bought himself a Jims Mowing franchise. He has never looked back (he is in the Canberra region). The money is good and the hours are excellent for him.
Please stay positive and best of luck.
'People are never perfect but love can be. People waste time looking for the perfect lover rather than creating the perfect love' - Princess Leigh-Cheri from Still Life With Woodpecker.