Putting aside some of the MN bias with respect to how things should work when the higher earner, name on the mortgage etc is male or female ...
It seems to me that your DH is making a fundamental mistake with respect to management of the business. I know, I did the same myself once.
That mistake is to mix or blur the lines between the business and personal finances.
He pays the business expenses on a personal credit card and, from the sounds of it, has the business income paid into a personal account (or one he treats as a personal account) or, even worse, takes cash without paying through a business account.
This is a recipie for disaster whether he invoices and gets paid on time or not - again I know as I was there when I first went into business. It allows a false sense of what money is what and allows you to put off things until the world comes crashing in “it’s okay if I use this bit for x as that bit i’ll Get in soon can pay the suppliers”
His accountant will have had conversations with him about it, mine was lovely and would roll her eyes at me and say “you really should not be doing that” along with various warnings about how HMRC or companies house could see things - but I did not listen until almost too late.
You need to meet with the accountant and chat about going Limited with both of you as Shareholders. There may be a way to have some of the money you have committed to his debts treated as an investment into the business and recoverable in a tax efficient way once he sorts the business side.
Your role should be a shareholder only, not a Director, if you do not want to get involved with the running of the business or potentially affected by any mismanagement issues in the future.
It will be painful for him to admit he has been doing it all wrong. It was for me, but he will have a huge sense of relief once it’s all sorted.
Get the accountant to set a salary for him. Base the split of your bills on that - the dividends etc can be split between both of you and put towards one offs like holidays etc which come just from your salary.
The business may be able to employ you to increase the efficiency of your joint drawings from the business but will depend on your income now.
The business should employ book keeping services from the accountants I..e have them manage the company bank account and pay wages, invoices etc.
Get a phone answering service to deal with all calls, new enquiries, customer service, supplier accounts etc - I use one which can do all this for £69 pm
Invest in some cheap software for generating invoices and quotes (loads out there and his accountant may have a favourite). My phone service will even call out chasing invoices if I ask them.
Like you say, it is about working smarter. He may have to face facts that the business is a bad one, but this would be a last, structured way to test it.
Hopefully it will be that he is, like many entrepreneurs, good at the fun, skillful bit but crap at the admin side. There are many people and services able to take this burden and it is not a sign of being crap at your business that you delegate this stuff out. I actually found it led to me being able to concentrate on the income generating parts to pay a relatively small amount to have someone take care of the admin.
I hope this is something you would both consider. If he can’t see this is a good option for the sake of both of you, your marriage and kids as well as his own sanity (as I say i’ve Been there) then he probably is in cloud cuckoo land and needs to get an employed position and hand over all the financial reigns for the time being