Am I legally responsible for half his credit card debt?

You have no liability to his actual creditors whatsoever unless you applied for the credit or co-applied for the credit or loans involved – that is to say Visa or MasterCard could not succeed in court against you for any amount if you never applied for the credit. However under the Family Law Act, as between you and your husband, you are each presumed to be equally responsible for all debt incurred by either of you during the course of your cohabitation if the expenses were incurred for a family purpose. The equal division can be reapportioned to achieve fairness (so if he has 70% of the total family income then he may end up with 70% of the debt as well. Also you do not share liability for items he bought on his credit card for himself and took with him on separation. Only for those expenses reasonably incurred to support the family as a whole ( ie groceries, clothing, vacations, dinners out etc)