I am sorry for your loss. If you signed or used the credit card in any manner personally, then you could be held responsible personally. Remember that your husbands estate will still be liable for his debts, and that may affect assets that you think are yours. You really should meet with a Florida Probate Attorney as soon as possible.
I agree with Mr. Farnsworth's answer as to your potential personal liability for the use of the card. But even if you had no personal liability, assuming you are his sole heir as surviving spouse, if the CC company files a claim against your late husband's estate, your inheritance of the estate will likely be reduced by the amount of the debt to the extent there is any probatable, non exempt property. I agree that you should see a Fl. probate lawyer.