You would not be liable for the taxes, but if the IRS tries to collect the taxes, they can go after his bank accounts and assets. So, anything you own jointly with him could be subject to lien or levy by the IRS. You may ultimately be able to recover the money or assets, but it could take awhile.
I recommend that your fiance get his affairs in order with the help of an experienced tax attorney immediately and in the meantime, keep your assets out of his name.
You are not liable for taxes for any year prior to your marriage. However, if your spouse owes taxes from previous years, the IRS could levy or seize bank accounts or other assets in your husband's name, even if your name is also on the account.
It depends upon the state you live in. For example, here in California a creditor can collect premarital debts from the community property of both spouses. We generally recommend a prenuptial agreement when one spouse owes taxes.
You need advice from a tax attorney in your state.
