if I send out invitations, they just say Jo Shmo and partner, and leave it up to Jo what sort of partner comes along. Individuals can call their significant others what they like, though personally I think husband and wife should be restricted to legally married couples of opposite gender (common-law marriages don't get treated the same by law), and if you're told old to be called a girl you're too old to be called a girlfriend. (Same for boys.) That leaves the long-term unmarrieds, and gays; I think 'partner' is fine for either, but you may have to explain whether the partnership is romantic or businesslike. Terms like 'my snugglebunny' are not to be used in high society.