...................... ok, so I see why that seemed tempting but uh. You realize that the fact that you felt you needed to bribe your husband with a wildly unfair distribution of access to money to keep his irresponsible decisions slightly less visible to you should have been a flashing neon red sign that something was wrong, right?

Like, he's not actually spending any less of the marital funds this way, he's just spending it without having to account for it to you while he gets full insight into every dollar you spend. If he deposited $800 every month into the account and then spent $900 that would not actually be different for your purposes than him spending his $800 of cash and then $100 from the joint account. Nor for that matter would it be different if he handed you $400 cash and spend his $400 cash and then spent $500 from the joint account, although IMO splitting the cash is the least unhealthy option of the three. No matter how you slice it, the problem is he's spending more money than you think he should.