He sounds awful. I could never live with a man like this. You have one life. What sort of message are you sending to your children about the way men treat women?
So the business is in joint names is that definitely correct? And you have 6 children with him. You work there but you don't get paid for it, are you sure about that? The tax rules changed recently that's why I'm querying it. If the business is in joint names, you own half the business and it doesn't matter if you're a silent partner or work there full time, it's half yours legally. To live, he pays himself a salary. He will probably also take money out in dividends for both you and him as this is a good way of getting money out of the business (although the rules have changed on this too). This will also be stated on your tax returns.
I'm only asking because if you do decider to separate, there may be more money than you think. And if you discover that the business actually isn't legally in your name, you've got longevity in this relationship and effectively what's his is yours. In cases such as these, I'd say get shot, divorce and take as much money as you can as you are a sahm (if you have no salary) and have 6 dependants. The business is his livelihood so you won't be able to take him for everything otherwise he won't be able to provide for you. This leads on to my next question. Does the business definitely make a good profit? It's just you say you're renting and haven't bought your home and I was wondering why.
In any case, I would get all of the financial information copied and filed in a very safe place: tax returns, his pay slips and p60 for the last 3 years, any shares he holds either in the company or elsewhere, savings, other investments, pension plan. He sounds like a right pig and if you do decide to split I think you'll be in for a fight. Doing this now and continuing to get copies of his financial information (as well as yours) will give you the chance to get all the information without him suspecting. Leave it till later and you may never get the chance especially if everything is in the office.
I'm sorry to hear you live with such a cruel man. 