It could be. If questioned, you would need to prove that he did not LIVE in your home at any point during the last 6 months of the year. So if he does stay there sometimes, you cannot claim head of household. If he hasn't stayed there AT ALL during the last 6 months of the year, then you should be prepared to prove that since you do have the same address.
I am assuming you have children that you support and you maintain over half of the cost of the house. If you do not, then you cannot claim head of household.
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