If you are not even legally separated, the IRS looks upon it as you are still married, likely joint taxpayers. Best follow the advice of several Freepers here and get a good attorney, preferably a female with the personnna of a man eating shark.
Yes, get a lawyer. You can ask that he pay for your lawyer, too, if you are not employed. You need to get a divorce and financially you will be much better off.
I know, I went through it.