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The IRS publications say "Your spouse didn't live in your home during the last 6 months of the tax year.".   It depends on how "live" is interpreted.  Usually that means more than an occasional visit, like when going on vacation, you stay in a hotel, you don't live there.

Considered Unmarried

To qualify for head of household status, you must be either unmarried or considered unmarried on the last day of the year. You are considered unmarried on the last day of the tax year if you meet all the following tests.

   1) You file a separate return. A separate return includes a return claiming married filing separately, single, or head of household filing status.

   2) You paid more than half of the cost of keeping up your home for the tax year.

   3) 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. See Temporary absences under Qualifying Person, later.

  4)  Your home was the main home of your child, stepchild, or foster child for more than half the year. (See Home of qualifying person under Qualifying Person, later, for rules applying to a child's birth, death, or temporary absence during the year.)

   5) You must be able to claim an exemption for the child. However, you meet this test if you can’t claim the exemption only because the noncustodial parent can claim the child using the rules described in Children of divorced or separated parents (or parents who live apart) under Qualifying Child in chapter 3, or referred to in Support Test for Children of Divorced or Separated Parents (or Parents Who Live Apart) under Qualifying Relative in chapter 3. The general rules for claiming an exemption for a dependent are explained under Exemptions for Dependents in chapter 3.

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