"I don't know if we are Unicorn Hunters or not. I was under the impression that term meant a heterosexual man in an established relationship with a bisexual or bi-curious woman, seeking a new bisexual woman. I suppose maybe it means any couple seeking a third member, and has nothing to do with gender. I think the confusion comes in that for a F/F couple to find a middle aged man willing to be intimate with two women seems a much less daunting task than finding this apparently elusive third woman. Maybe I'm way off base on that one."
People use the phrase in different ways, and there's been vigorous debate on the boards before, with no resolution, on the exact definition. Some people focus on the typical m/f couple's search for the mythical hot bi babe... but such an entity is NOT mythical... I mean, I'm bi and not un-hot (and I've got a thing for couples to boot!).
So, to me, gender is not the significant thing, rather it's the often-problematic behavior pattern of seeking out a person who can fill a pre-determined niche by "joining" a relationship with an established couple and forming a perfect equilateral triangle. Such a person, who can love two members of a preexisting couple equally, be loved by them equally in return, integrate seamlessly into their lives without significantly changing the life they've built together, not want to get involved with other people, and suffer no feelings of insecurity or jealousy around being the "junior" member of the new triad... THAT individual is the mythical creature, in my eyes.
In terms of what I just described, it doesn't matter whether we're talking two women and a man, two men and a woman, three men, three women, or some combination of genderqueer individuals... it just ain't realistic or wise. It's that behavior that I think constitutes a clear pattern that needs to be identified and pointed out to both people doing it and people being targeted by it, and therein lies the utility of having a shorthand phrase to describe it. Sure it's usually an m/f couple seeking a woman, but I've seen various variations on the gender combo's doing the same.
Since you and Pidge aren't thinking of being involved with both of you as a requirement, merely as a preference... well, I'm no judge or arbiter, and as I stated above this is a term which doesn't even have an agreed upon definition to begin with!... but I'd say you're NOT "unicorn hunters". Nevertheless, since you're engaging in behavior that is at least somewhat similar, it's probably good to be aware of the trope and of the associated pitfalls, so that you can be sure to distinguish yourself from people who really are hunting unicorns, and to avoid said pitfalls.