>What the F am I supposed to do?!!!
Do as PP and others have suggested. Print off a list of all ebay transactions, decide which are yours and which are his, and then marry then up to your ban/card statements to see which you paid for. Them give him a list to check he agrees. If agreement can't be reached you may have to accept a loss or accept that he could accuse you of using his card for your purchases.
And remove his card from your account.
It's not an ebay problem so I wouldn't look there for help- it's for you two to sort out.
Good luck