Instructions exist to instruct you.
You can check the box on line 1 if any of the following was true on December 31, 2011.
• You were never married.
• You were legally separated according
to your state law under a decree of divorce or separate maintenance. But if, at the end of 2011, your divorce was not final (an interlocutory decree), you are considered married and cannot check the box on line 1.
• You were widowed before
January 1, 2011, and did not remarry before the end of 2011. But if you have a dependent child, you may be able to use the qualifying widow(er) filing status. See the instructions for line 5.
Married Filing Jointly
You can check the box on line 2 if any of the following apply.
• You were married at the end of 2011, even if you did not live with your spouse at the end of 2011.
• Your spouse died in 2011 and you did not remarry in 2011.
• You were married at the end of 2011, and your spouse died in 2012 before filing a 2011 return.
For federal tax purposes, a marriage means only a legal union between a man and a woman as husband and wife, and the word “spouse” means a person of the oppo- site sex who is a husband or a wife. A husband and wife filing jointly report their combined income and deduct their com- bined allowable expenses on one return. They can file a joint return even if only one had income or if they did not live together all year. However, both persons must sign the return. Once you file a joint return, you cannot choose to file separate returns for that year after the due date of the return.
Change references to 2011 to 2012.
In short, you are not allowed to file as single. See the first line.