I too, am an "attention whore" like GermanChick. While I have participated in MMF sex, it was with two straight guys who were all about me. Looking back, it turns me on to think about what it would have been like if they had more interaction between themselves instead of just focusing on me.
Would I want to be in a relationship with a man who is bi? Don't know about that. As in any relationship communication is key, however, with a bi man, I think it would have to be even more important. While there is a host of toys available now, would that be enough for him? How often would he need to be with men? Is this an open relationship? To me, there would be too many factors involved, and I don't know if I could deal. Competing with a another female is one thing, another man...no competition.