A shareholder isn't necessarily an employee, so OP can have been a shareholder, but not earning a salary from the company. I have seen the company's accounts, which do state there is only 1 employee (OPs STBXH).
And CMS calculations can include any dividend income he has as well as salaries. You just have to ask for extra income to be taken in to account - HMRC link
I have a client that wanted me to figure out whether he would have to pay less CMS if he was on a salary versus his dividends.
The calculations seemed to work out quite equal as salary would generate a higher personal tax bill, so his salary would be higher than his dividends to generate the same monthly income.
The CMS calculation on the higher salary was very similar to what he was already paying based on dividends, so the system did seem to work OK in this respect.
(And yes - I lost a lot of respect for that client for asking me to do the calculations!)
If, however, OP's STBXH dividends are reduced because he's been declaring half of them as OP's dividends, then that could cause a miscalculation in his CMS claim, but in future if he accounted for them all as his own income the CMS figure should go up.
He will likely try and keep his official income to an absolute minimum to avoid paying too much maintenance though.