I was in what I would call a "monogamish" relationship with my partner L - we were committed to each other, but allowed to flirt, cuddle with, kiss, and dance with whoever we wanted, and were very open in talking to each other about other people we had crushes on. We met K, who is now our third, at a weekend retreat for queer students from our college campus and the other local colleges, and hung out with her a bit. She and my partner started to talk on Facebook a lot - they have similar "night owl" sleep habits - and it developed into a mutual crush, which L admitted to me. I was delighted by this, and somewhat surprised by my own delight, since a crush with potential to go somewhere was not something we'd experienced as a couple before. I started talking to K more as well, and it was easy to understand why L liked her so much - I started to get a bit of a crush myself, which she reciprocated. After a few three-person dates and cuddle sessions, we invited her to go to a dance with us, then brought her home and had a threesome. We all realized our feelings went beyond purely sexual and worked on establishing a triad relationship. It's new, but so far we are all very happy with how things have turned out.