Fortunately, by the time these initial language problems become good and boring, a solution stands ready: the couple can choose to become "fiancé" and "fiancée." Or, to be quaint, "betrothed." With only a little paperwork and clergy or a justice of the peace, they can start referring to each other as "husband," "wife," and "married." And then they can tackle the problem of what to call each other privately.
Most longtime couples have private names for each other. Sometimes these names slip out in the presence of others, in times of stress, exhilaration, or PR spin, or after everybody's had a few drinks. My friends Anita and Jim call each other Frank. George W. and Laura, as their daughters announced to the world during the Republican National Convention, call each other Bushie. A dog-loving couple who will be nameless here because I need to remain on speaking terms with them call each other Wooda (that's a phonetic rendering) and Wooba, short for "Wonder Dog" and "Wonder Bitch." My friend Robin calls her husband, whose name is Richard, Lord Voldemort, a.k.a. "He Who Must Not Be Named." That's when she's not calling him Wally (this is a good story, but a long one).
And my husband and me? Since you asked, we call each other "my pet" or Pet. "Pet, would you turn the music down?" "Yes, Pet." As a, um, pet name, it's minimalist (our aesthetic), it's egalitarian, and it's entertaining--to us, at any rate. Partly for fun and partly to keep straight which of us we're talking about, we have variant names as well. For instance, if we are visiting California or drinking Sonoma Valley wine, Julian (that's his real name) is Petaluma.
We have many variants, and the list of them keeps growing, but you get the idea.