I think it's more than just living in the same house. I think you pass the test if you have a joint checking account, maybe have both your names on an apartment lease or on a mortgage, etc...
I used to work for a company that checked to see if employees lived together. They would run a report to link employees who had the same address, but were not listed as married. As a matter of fact, the advice was, if you do live together with another employee, make sure you used a PO Box for your mailing address.