Sadly, such cases are not unfamiliar. If you can prove that you were living in the property, and that it was your homestead property at the time of the mortgage, then you have good equitable grounds. However, even then, a lot is going to depend on the circumstances including your knowledge if any that the mortgage existed, and whether you benefited from the funds he received from the lender. From prior research in such cases, I believe the likely best outcome is that although the mortgagee bank can not foreclose you, they would still have a mortgage interest as to your husband's 1/2 interest even though it was homestead property. So, if you sell, then you would have to pay 1/2 the funds received to the mortgage lender up to the point they are paid in full. The other 1/2 is yours, and any money left, if any, from your husband's 1/2 after paying the mortgage. You can not get your own mortgage without paying off that mortgage, but you might be able to get a court to limit how much the mortgage lender is entitled to as its pay-off amount if you can show your husband's 1/2 would not be sufficient to pay them off and you need to put a mortgage on the property. It's possible, but not likely, that you will get the mortgage voided entirely if you can show complete oversight by the lender. Lastly, If you can't prove that you were living in the property and it was your homestead to the exclusion of any other property, then forget about it, you will lose.
The law is complicated and although the facts expressed may seem to be all that is relevant, there may be many other important facts to consider. Also, the law is constantly undergoing change, so what may be correct today, may not be accurate tomorrow. Only a full consultation with an attorney experienced or knowledgeable in the specific legal subject matter is likely to result in the optimal course of action.
Reverse mortgages are like any other mortgages in that the Florida Constitution requires that both spouses must sign mortgages of homestead property. If you did not sign the reverse mortgage, it is not enforceable. If you did sign the mortgage, its provisions may provide that you can remain in the house for your lifetime. You should consult an experienced real estate lawyer in your area. You lawyer can review all of the documents and advise you of what your rights are.
Disclaimer: This answer is provided for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Actual legal advice can only be provided after completing a comprehensive consultation in which all of the relevant facts are discussed and reviewed.