I don’t know the full circumstances OP, and it doesn’t sound easy.
A problem gambler will be fighting a losing battle to cover up the losses, desperately trying to make the money back in a never ending cycle that just drives them deeper and deeper into despair and debt.
Whilst this is all going on they will be doing everything to keep a lid on it and not draw attention to anything financial, whilst trying to appear ‘normal’
This gets incredibly stressful and any form of perceived attack on that person will make them shut down more.
The movement of money from the joint account, removing his salary from being paid into it and then hiding of money points strongly to a gambling addiction. It’s easy to look at this that he’s being sneaky or hiding money, which he is, but probably due to the reason that he’s lost control of the debt and is desperately trying to sort things out.
You will get more out of him if you approach this by trying to understand, tell him you’re willing to listen and sort this out together as a family. That’s there’s nothing so bad that can’t be sorted out.
The reason why I say this, is because I was a gambling addict. I lost my house, my savings and was in a huge amount of debt that I just gambled more in an attempt to clear.
Someone telling me they would find a way out of this with me was what helped more than anything. I paid, and continue to pay, the debt back entirely alone as I feel it is my responsibility to do this.