A word that describes people who dates two people? How about, oh I don't know, polyamorous?
I, for one, date PEOPLE. If those people happen to be a man and a woman in a partnership, they're still "people" first and "a couple" second.
It's impossible to "date a couple." A couple is two people in a relationship. A relationship is an abstract concept describing the association between two individuals. A relationship is not a person with thoughts, feelings, and an identity. You cannot date an abstract concept, you can only date real live people.
Realistically, if a couple has "desires that aren't prestent in the existing dynamic" then throwing a third person into the mix is more likely to cause jealousy than be "sort of filling in." Having it shoved in your face that you're not meeting your partner's needs, and then having those needs be met right in front of you, is extremely unlikely to cause compersion... especially if your own desires for the third person are not as strong as your partner's.
The notion of being a unicorn and only "dating couples" is as problematic as being a couple and only dating unattached women who will love them both equally. It's a nice notion, but in practice, pretty much every self-proclaimed unicorn runs into the same problem: real emotions don't care about your ideals.
Each and every successful triad I have ever heard of has come about by coincidence, not intention. When it works, it "just sorta happens." No one was deliberately trying to form a triad.
You can't force yourself to love someone. Labels aside, this whole thread is a case in point. Right off the bat, she was closer to the woman than the man. She and the man made a conscious effort to "build" their relationship, trying to learn to love each other more. Unsurprisingly, it didn't work out.
This thread is not an exceptional chapter in a book of successful unicorn love stories. This is exactly the way it turns out MOST of the time. I'm not saying triads can't work and I'm not saying a woman can't successfully date a couple. I'm just saying that USUALLY it doesn't work out that way. It's an objective observation of the statistics. And yet, ironically, here's a bunch of people coming to the defence of unicorn-hunting and unicorns when this whole thread is a prime example of why seeking an ideal over individual relationships is unlikely to succeed. You're only serving to reinforce her confused notion that you can force triads to work if you only push at it hard enough, or keep looking until you find the right one.
The biggest problem with the way triads are usually attempted is that people force their emotions rather than letting them develop naturally. Three people get together and declare "we're going to have a triad, and we're all going to love each other equally. Here are the parameters we're going to establish to make sure everyone gets fair treatment and no one ever feels left out." But real hearts don't work that way. You can't turn it on and off and adjust the voltage as prescribed by your Triad Agreement. Rather, your triad agreement has to be able to adjust based on the actual feelings of the people involved.
Anyone in a successful triad will tell you how important it is to be flexible. Allow things to progress naturally. Accept that sometimes, partners A & B will be closer than A & C, and at other times B & C will be closer. Let it flow. Accept that the triad may form even a vee and allow each arm to be happy for the other if that happens. Place your love of the individuals above your love of the triad ideology, and put the individual happiness of your partners above your attachment to a particular outcome.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker