My spouse and I own a house where we’ve lived together for a few years but I am currently renting an apartment in a nearby town where I work. Would we be living “separate and apart” if
• She stays in our house during the week and she stays in the apartment on weekends.
• I do the opposite (i.e. I stay in the apartment during the week and I stay in our house on weekends).
• We don’t stay in either place together at the same time.
• We don’t see each other except possibly once a week for lunch to keep in touch (there is no animosity).
So long as you are not living together as husband and wife your separation is valid, even if you are switching residences.