You're not a unicorn hunter. You're the unicorn. Unicorn hunters are couples looking for a single bi woman willing to be in a relationship with both of them. That's you.
As for her, she is happily in a monogamous relationship, and from your post, if I'm not mistaken, he was cheating on her. I can see why she wouldn't trust you. Even if she was comfortable with being in a triad, it probably wouldn't be with you.
As for him, he broke up with you, and there is no reason to believe he wants to be in a triad with the two of you, either, especially if he was hiding you from her.
You're not with either of them, and as far as I can tell neither has any desire to be in a relationship with you. Drop it. It's not about turning someone into a unicorn, it's about making to people who are happy together (and, it seems, content to stay monogamous at this point) want to both be with you. Which right now neither of them does.
Just let it go, it's not going to happen.