You could either file single, or head of household if you have dependents.
From Publication 504 https://www.irs.gov/pub/irs-pdf/p504.pdf
You are considered unmarried
on the last day of the tax year if you meet all the following
tests.
• You file a separate return. A separate return includes
a return claiming married filing separately, single, or
head of household filing status.
• You paid more than half the cost of keeping up your
home for the tax year.
• Your spouse didn’t live in your home during the last 6
months of the tax year. Your spouse is considered to
live in your home even if he or she is temporarily absent due to special circumstances.
[Edited 4/15/2015 | 9:53 PM est]
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