Good question!!! And it’s not nearly as straightforward as one might imagine.  First of all, the IRS doesn’t recognize couples living together – regardless of sexual orientation or state law – as being married.  Additionally, you can use for you filing status married filing jointly if any to these conditions are met:  You were married as of December 31, 2007 – even if you were not living with your spouse at the end of the year; Your spouse died in 2007 and you didn’t remarry in 2007; or Your spouse died in 2008 before you were able to file a 2007 return.  In the case of death, you are exempt from the “both must sign” rule.  Sign you name and write “surviving spouse” after your signature.