roommate
POSSLQ
https://en.wikipedia.org/wiki/POSSLQ
https://www.wikidata.org/wiki/Q7120037
A person of the "opposite" sex (a man living with a woman or a woman living with a man) with whom one shares living quarters.
United States Census Bureau
people of opposite sex sharing living quarters
person of opposite sex sharing living quarters
persons of opposite sex sharing living quarters