From Longman Dictionary of Contemporary Englishlive-in lover/boyfriend etclive-in lover/boyfriend etcLIVE WITH somebodysomeone who lives with their sexual partner but is not married to them → live-in
Examples from the Corpus
live-in lover/boyfriend etc• Two divorces, a long string of live-in boyfriends.• She took no new live-in lover, and as far as she was aware, neither did Charles.• She met her live-in boyfriend on-line.• She had a live-in boyfriend to whom she devoted most of her time and energy. 