what is worst is that it is in YOUR credit account! DH and I have each other's bank/card details, and use them quite a bit depending on who is more in the black at the time. But we always check first - the only exception being if it's under about a tenner and it's something essential (groceries).
We share all money, but especially as we are not well off, we always discuss big purchases. £100 on a few clothes is ridiculous if you're in debt. What a knob.
Is he depressed? Retail therapy? Or is he just a financial ostrich, so to speak?