I am so sorry for your loss -- may you have the strength to survive this ordeal.
If you filed jointly for thos years in question and unless you can show that you had no knowledge of what was done etc. etc., you are liable for his tax debts. Best thing to do is call the tax board and talk to them as to your financial situation and that it would cause you great harm if you had to pay these amounts ( -- they may atleast be willing to help with the interest and penalties and even the actual tax owed)
Good Luck
