Serioso

A term for one's significant other, to be used by adult heterosexual couples in long-term or lifelong, monogamous relationships who are serious, live together and have built their lives together, but have yet to get engaged or don't intend to marry at all.

Where "boyfriend/girlfriend" is too childish, "husband/wife" doesn't apply, "fiance" is dishonest, "partner" sounds homosexual and "lover" is too sexual, there is serioso. Coined by Chemda of the Keith and The Girl podcast, episode 130.