"Partner" is a mostly term used with gays. straights many feel strange to apply this term to husband, also wife. Can someone not simply ask about "spouse"? There previously exists term without gender for such persons.
I've seen "partner" being used in reference to hetero relationships more frequently in the last decade, and think that's probably a good development. "Boyfriend" and "Girlfriend" sounds a bit infantilizing to me when used in reference to adults.
One argument in favor of using partner is that boyfriend/girlfriend is ambiguous. My wife often refers to her close female friends as "my girlfriend", even though they are clearly not dating each other. It occasionally causes some confusion with people a generation older than us who aren't familiar with that usage.