To me the distinction between all the terms for your other half can be equated to, interestingly enough, the words for shit.

The aforementioned term is obviously more vulgar, "waste" and "excrement" too broad, "feces" too formal and "stool" too medical, and, to state the obvious, "poop/poo", while perfectly normal in everyday conversation, still has a juvenile twang to it. In short, for me there personally isn't one term for this enigmatic substance without clinical, vulgar, or otherwise unnecessary connotations.

To get back on track, "boyfriend/girlfriend" again sounds very much like what high schoolers would say (no shade to grown adults who use it — it's the connotations of the term that sour it for me), while obviously fiancé(e), husband/wife, and spouse have immutable definitions. I don't think many more labels for this type of relationship exist, and as an incurable romantic, the idea of someone being your "partner", whether in work, love, or life remaining unspecified, feels right to me. Therefore, in the context of LGB issues, I have no problem with straight people using it. (However, as a young'un I haven't really seen many of them try to pretend they're homosexual, so I wouldn't know what to make of that and indeed I don't as of now.)