How do I file if I'm married but haven't lived with husband for over five years?

[ee-ea]

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[ThomasM125]

If you are legally married, your only filing options are married filing joint, married filing separate or head of household (if you qualify for that.) You cannot file as single.

To qualify to file as head of household, you have to be providing over half the cost of a household in which a qualifying dependent lives, such as your minor child.  Here is an article that will explain more:  Head of Household