If you are considered married you and your spouse can file a joint return or separate returns.

You are considered married for the whole year if on the last day of your tax year you and your spouse meet any one of the following tests.

1. You are married and living together as spouses.
2. You are living together in a common law marriage that is recognized in the state where you now live or in the state where the common law marriage began.
3. You are married and living apart, but not legally separated under a decree of divorce or separate maintenance.
4. You are separated under an interlocutory (not final) decree of divorce. For purposes of filing a joint return, you are not considered divorced.

For more information see IRS Publication 17 Your Federal Income Tax (For Individuals).