Attracted to 2 Genders ... Married to 1 Person?

So I got to talking with some friends today and the question was raised: Can someone who is bi- be in a committed relationship with one person? Say this bi-sexual being is a female (because, let's face it, my point of view rarely varies to the male point of view). If she decides to marry a man, is she now straight? Ok, ok... maybe she's actually loyal to him and doesn't cheat, a rarity in this day and age, I agree. But let's just say, for the sake of this debate, that she is, indeed, faithful. Is she straight because she married a man and will never again be with a female? What if she still has sexual fantasies about females, but just doesn't act on them? Is that what makes the difference? After raising this question to one of my guy friends - 'Can someone who is bi- ever be in a committed relationship with just one person?' - his response was - 'Maybe people can just be content with being with one person'.  Ok, ok. I get it. But for me, I'm not so sure I can ever really be content with one person, and one person only.  Maybe it's partly due to the fact that it took me approximately 20 years of my life to realize I was bi-sexual (and that is definitely a whole other debate for another day!!).  Maybe I want to make up for lost time. I'm not sure, but for me : 2 attractive genders > (is greater than) 1 committed relationship : therefore, not = (equal).