Then why are you bothering to work for it? There's tons of flexible min wage jobs around, get one of those or better still, get a job that matches your earning potential. You're not a minimum wage person you have greater capabilities. If you get back to work ASAP, not when DC goes uni, you'll be able to pay the interest accrued on the credit card. The business is both of yours so why do you have to work there for peanuts? The reduced tax paid due to your low wages suits him, benefits him. I'll bet the job you do for the business isn't even a min wage type job too. All suits him. Go work for Tesco or McDonald's or something and get a better deal.
Your DP is financially abusive with the restricted access to money, not given enough for household expenses and the lifestyle he expects you both to lead and the refusing to discuss it. That he has reasons for his behaviour and thinks he's being reasonable doesn't change this. He isn't being reasonable. It may surprise you to know all abusive people think their reasons for being so are perfectly ok.
Money isn't being split 50/50, that's after he's creamed off the bonuses and paid for the DSC (who aren't your financial responsibility at all). So you're receiving less than half, less than you would if he funds his DSC and personal savings from his own 50% .
He's got a set up where all family expenses are paid on a CC in your name so the final bill stops with you. This should be a joint card for which he's jointly responsible for the bill. That would be fair, the current set up isn't.
He gives an allowance for basic family costs then adds on expenses, beauty wishes he has for you and entertainment costs for friends, then expects you to pay. That's out of order, OP.
And you're too afraid of his reaction to tell him "hey great our friends coming, but the weekend will cost eg circa £300 and there's only £100 left on the CC limit which is needed for DC new shoes, so please give me £300 or I can't shop for food for friends and we'll not be going out". He's using your embarrassment to prevent you saying anything to friends and forcing you to pay up out of your own pocket. It's manipulative.
Yes he is nasty. You're afraid of his reaction. That's not because he's the picture of reasonableness, all sweetness and light. It's because he displayed temper if he doesn't get his own way. And you're altering your own behaviour to avoid that. This is what abuse does to you, that altering of your own behaviour and also you being convinced it's all your own fault when it isn't.