Filing Status Quandary

Legally I am married, but my wife and her 3 kids have not lived in my home since June 30.  The IRS considers me unmarried.  However, when I select Married I'm only given the option to file as married filing jointly or married filing separately.  I don't believe I can select Single or Legally Separated (no legal paperwork filed) as my marital status.  HELP!  I was under the impression that I could file as Head of Household but that is not an option if I select Married as my marital status.