If your married and have a dependent you can file Jointly or Separately.
You can also file as Head of Household if your are "considered unmarried" as of the last day of the tax year. To be considered unmarried means:
- You file a separate return
- You paid more than half of the cost of keeping up your home for the tax year
- Your spouse did not live in the home during the last 6 months of the tax year
- Your home was the main home for your child, step child, or foster child for at least 6 months of the tax year
- You must be able to claim the child as a dependent
Keep in mind that if you and your spouse lived in separate homes due to a temporary circumstance, such as military service, business trips, a stay in a medical treatment facility, or attendance at college, the IRS still considers you married for that tax year.