I've never had a girlfriend/wife that wasn't. I personally can't imagine not being at least bi-curious. I don't think I really can imagine what pure mono-gender attraction would be like. I mean.... nah. No, idea.
I like it when my wife positively comments on a hot chick we see in the street. It makes me warm and fuzzy inside. Its just one more example that her cup is half-full.... Yeah... that's why bi-sexuality beats straightness! It feels more like an embrace of life.
Bi-chicks rock!!!