london - ha!
Speaking from within a not-yet-triad situation, I can say (based on an earlier comment by london, I think, plus something Natja said) that one of the NICER things, for me, is that I'm not the sexual centerpiece. That whole porn MFM thing? Yeah, not so much.
When reading around, my wife gets irritated by the suggestion that she "became" bi to please me. Yuck - the concept is awful. It doesn't describe her and her "mostly straight" ways. She doesn't see herself as bi or poly, not at all. She has a girlfriend, but even the word "girlfriend" bugs her. AM is part of her life, they make love, are best friends, don't name it, it's just AM. AM feels the same way toward her.
Frankly, neither wants to be associated with "poly" when they see the attitude of conversations on boards like this. It's one reason this thread is interesting to me, seeing the space of responses, but I'm different from the two of them...