I think the first mistake you can do on an unicorn hunt is to treat people as 'prospective unicorns' instead of people. I think there are other women out there looking for love, and to be given a set of rules and limitations you have to meet BEFOREHAND in order to be lovable is the best way to arouse disinterest in the unicorn you want to court.
From what I've read in your 'Chinese Gangs' thread, you might have just stumbled upon an unicorn survivor of your particular train wreck. As you see, a pure accident. Very unlikely. Human chemistry is. Or you can totally disregard all and any advice you receive and just go on OkCupid, which is what I did, and the results so far have not been disastrous. Again, a pure accident.
I think many unicorn hunters would sleep better if they would consider at least three things before embarking on their hunt;
1) Your unicorn might be in a primary relationship already, and not interested in moving in with you.
2) Your unicorn might have a busy social life of her own and not be interested in forsaking all her other connections to be with you.
3) As redpepper pointed out, you might have a lovely vee situation developing, which will surely go all to hell if you force it to become a triad.
I would feel totally put off by having to act as a sexual resource to the other person in the couple just to make sure they don't get overly jealous of my connection with their partner. In love all things are not equal; you might be the best of friends, even FWBs, with the other partner but really IN LOVE in the ooshy-mooshy way with the other partner.
Me: bi female in my twenties