If you find that he's using the "joint" card entirely too much, call the card company and report the card lost. Request that the remaining balance be transferred to a new account number. If he remains on the joint card, you will be liable for any debt he incurs for the time being.
I wouldn't ask him to get a separate card, I would just go ahead and either have your name removed off the joint one or open up a new one, but the only thing that matters is that your name isn't on the same account with his name...you don't want to be paying his debt off as well as what may already be on that card.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
