One of the oddities of the English language is that though many words have multiple synonyms, and we have words for many things we rarely refer to, one of the most ubiquitous concepts in American society has no name: There’s no ideal term for an unmarried party in a romantic relationship.
This glaring omission is partly due to the fact that open societal acknowledgment of unmarried parties — let’s just go with the acronym UPIARR for now — especially those who have no intention of marrying, is a relatively recent phenomenon, but it seems that our culture should have settled on a satisfactory label by now.
The reigning placeholders to describe UPIARRs, in the absence of universally accepted terms, are boyfriend and girlfriend. Despite the fact that my fellow UPIARR and I are AARP members, we have no problem with the terminology — the juvenile connotations of these words is obsolete — but other people, especially those of a certain age, are uncomfortable with them. Unfortunately, the more mature-sounding “man friend” and “woman friend” are clumsy and imprecise.
Paramour (French for, literally, “for love”) is unfortunately unsuitable because its connotation is of illicit love. Lover implies a focus on sex, and most pet terms (darling, honey, sweetheart, and the like) are too intimate for some social situations; informal phrases like “my guy” and “my girl” have the same disadvantage. Beau (from the French word for “beautiful”) is inoffensive but seems too glib and, despite the etymology, is an exclusively male term.
Mistress has a longstanding connotation of “a kept woman,” though for some time, because modern women can more easily maintain financial independence, the term has referred simply to a woman in a romantic or sexual relationship with a married man. But this word has no utility outside of references to marital infidelity.
Suitor is too stiff, does not imply an established relationship, and traditionally denotes a man. “Significant other” and “life partner” both have an artificial, passionless taint, as if inspired by bureaucratic policy. “Domestic partner” shares that disadvantage while also assuming cohabitation.
The prevailing alternative to boyfriend and girlfriend is partner, though the use of this word in other contexts, such as business, makes it unhelpfully ambiguous. “Life partner” imposes the implication of a lifelong relationship.
My favorite humorous designation is “undocumented husband/wife,” but even that implies that the ultimate goal of the relationship is marriage and it isn’t of much use in straightforward contexts.
In most social situations, the simplest solution is to introduce your fellow UPIARR by name only and let nonverbal signals do the rest. However, this website is about writing, not about oral communication, and effective terminology depends on the context of the written communication, so writers must make their own decisions about how to refer to their own UPIARRs or others in that role.