collaborator, cooperator, mate, pardner, spouse, consort, married person, parter, partnership, husband, more...

rival, opponent, adversary, enemy, competitor

spouse, significant other, boyfriend, girlfriend, roommate, best friend, co-worker, parent, child, sibling, more...

senior, new, sexual, junior, general, male, former, equal, female, limited, silent

other person,   other batsman,   western sidekick,   spacex collaborator,   form a couple,   make a coinvestment,   male companion,   dynamic duo member,   other in dancing,   form an alliance