Edit: here you go, directly from IRS publication 501, which explains the filing categories. Note that you must meet ALL three requirements.
"Head of Household
You may be able to file as head of household if you meet all the following requirements.
You are unmarried or “considered unmarried” on the last day of the year.
You paid more than half the cost of keeping up a home for the year.
A “qualifying person” lived with you in the home for more than half the year (except for temporary absences, such as school). However, if the “qualifying person” is your dependent parent, he or she does not have to live with you. See Special rule for parent , later, under Qualifying Person."