If you’re already shacking up, then “my old man” or “my old lady” are the traditional terms. If you haven’t yet done that, then the following would work:
“Suitor” is acceptable to refer to a gentleman.
“My darling Miss <<name>>” or “Miss <<name>>” would be suitable to refer to a lady. Use of “my darling” would indicate closer than ordinary familiarity.
Call him SLAVE and he can use DOMINEX. 
[sup]Or vis-a-versa[/sup]
How about just calling him your friend. If introduced in a social situation, most people will guess. Partner is too business and sig. other is too wordy
Your right, I am 31 female and I don’t want to be called a girlfriend. Just like I don’t like the term boyfriend. I would rather be refered to as “friend”. And in the context, I think most people can guess what it means.
Besides, it doesn’t matter what you call each other, it is how you treat each other 
There is nothing negative about the terms boyfriend and girlfriend; anyone who dislikes them is reading too much into them or projecting personal insecurities onto them.
Significant Other is a fine substitute. 10 years ago it might have sounded clinical, but nowadays I think most people hear it as a normal term refering to a boyfriend or girlfriend. And SO saves bandwidth on the internet.
This whole thread reminds me of that Cheers episode when Frasier announces that he and Lilith are becoming POSSLQs (pronounced as “posselcues”). Two points for the first person to expand that acronym.
The first part must be “persons of opposite sexes” but damned if I can figure out the rest of it.
Anyway, I’ve always preferred the term sweetie or sweetheart. It’s definitively romantic without getting into the whole status of the relationship thing, and it’s neither geriatric-sounding nor juvenile.
He’s your gentleman caller.
What a beautiful, Beautiful Name.
Person of the Opposite Sex Sharing Living Quarters?
My…Well, Brad and I struggle with this on a regular basis. It’s come up more lately since we’re in the process of buying a house. Since he’s 50 and I’m 36, we feel a little beyond the girlfriend/boyfriend thing. Concubine and consort have been used–but not on any official documents!
I’ve always wanted to use paramour after reading it in many old novels. I just like the sound of it. Looking at the definition I see that it’s now meant in a bad sense, like in an adultery, which is a shame because it used to be so nice. I’ll probably use it anyway since I don’t think very many people will hear the bad meaning. Maybe we can take it back.
I knew a couple years ago who referred to their partners by the Spanish word “alternativa” as in alternative to a wife, husband, boyfriend, girlfriend whatever.