As a newbie, it really helps to read all these responses. Thanks everyone :-)
I like the term 'Situationally Bi', as it sums up my few experiences with men. All three have been in the presence of a woman as well, and I found that being the third member to them as a couple compelled me to be their plaything of desires. I had never thought that I was Bi until during the first experience, when I was in a situation of wanting to kiss her. She was giving him oral at the time, and she stopped and said 'do you want a turn?' I just went with it and it was great fun seeing how they both reacted. They seemed to love it, and so did I. From that point on I realized that I played for both teams, but because I don't actively seek out men, or imagine living with a guy, I believe that my bisexuality relies on the situation. Great term, and discussion. Thanks.