Dear unicorn seekers,
From what you wrote, I am not sure if you are only looking for a long-term sexual partner for threesomes, who will not become emotionally involved, or someone to be a romantic/love partner also. Your post does come across like you are only looking for threesomes, so I gotta wonder why you came to a polyamory site for that. But if you are open to more than sex, here is some info on unicorns and unicorn-hunting that, hopefully, will help you...
First of all, unicorns are mythical creatures. They do not exist. Just because a bi woman is, has been, or would like to be, in a triad doesn't mean she is a unicorn - to call her that doesn't make sense if you think about it. If she exists, she can't be a unicorn! The terms "unicorn" and "unicorn hunter" came about in poly circles as a way to illustrate the futility of the very unrealistic dream certain couples always seem to chase after - basically it is a put-down, directed toward the couple, which is usually a male and female, and married. The stereotype is that the mythical "hot bi babe" (or HBB) is always expected to love both partners equally (as if you could order your love like a sandwich at the deli), move in with them, share in household chores and childcare, service both of them sexually, and not have any other relationships with anyone else but them. No self-respecting single bisexual woman would voluntarily call herself a unicorn, knowing this. The phrase is derogatory (against the couple).
And here's why: many newbie couples want to find a HBB to fulfill a role that is focused on satisfying
their desires, AND they tend to operate as if the couple is one unit, and not two individuals (gah!). The "unicorn"/HBB is expected to "join their relationship" instead of individually exploring the potential relationships before them at her own pace (remember, there are four different relationships that can evolve separately over time among three people) and according to her own heart. It's a "Two Plus One" mentality, which is rather distasteful. If three people are in a triad relationship -- in reality, it is "One Plus One Plus One." And the couples always seem to forget that it isn't only the HBB who could develop more intense feelings for only one person in the couple and not the other - but one of the already established couple could find themselves enthralled, euphoric, and developing very intense feelings for the HBB. Suddenly their long-established partner feels unwanted - or "left out" because they believe they
have to be included in everything all the time! No autonomy allowed! Ugh.
Anyway, it's not that great relationships can't happen among three people, if developed naturally, nor that there aren't any single people looking to be in relationship with a couple. It's that "seeking a unicorn" is a ridiculously impossible ideal to realize. Whenever we hear about relationships of three or four people that succeed (and they do!), it is always that those relationships "just happened," and simply "fell into place," and are
never the result of advertising for a woman to fit into their lives like a puzzle-piece. Unicorn hunting is not something to aspire to or be proud of. Of course,the term isn't applied to every couple that gets involved with a single bi woman, but when it is used, it is a criticism of their approach -
prescribed, instead of naturally occurring.
See, anytime you put emphasis on a role first, and then try to fit a person into that role, it will most likely fail - and disastrously so - simply because fitting a human being into one's unrealistic expectations about how the person and the relationship should go, negates that person's individuality and denies a natural progression in relating to others. This applies to many relationships, not just the unicorn-hunting ones.
So, again it isn't a triad, per se, that is mythical or never works out if it happens naturally instead of in a prescribed way. It is the fantasies of the unicorn-hunting couple, not the relationship configuration nor the actual woman herself, that is a highly unrealistic pipe-dream.
I recommend you read the following threads for some more info and enlightenment. They contain contributions from people on both sides of the equations:
Added to, Joining In
Why Is it So Hard?
advice for couple seeking third
What's in it for a unicorn?
I Hope I'm Not Naive
Hope this helps in some way.