According to IRS rules, to be considered unmarried you have to "live apart from your spouse for the last 6 months of the year, file a separate tax return and pay more than half of the cost of up-keeping your household. You must also have provided the main home for your child and be able to claim this child as your dependent." In this case you could file as Head of Household. If you are still living together, then you couldn't file as unmarried, but you can file as 'married filing separately'. You will need a 1040 form for that.