If I may: bisexuality is being attracted by people of both genders.
But it is not really very different from any other attraction. It is no more of a "deviation" than it is to find both blondes and brunettes atractive, and has no more moral or behavioral consequences.
Sure, bisexuals may be unfaithful, promiscuous or sexually compulsive. It is even conceivable that there is a statistical or even causal correlation. But I am not aware of any, and intuitively it just looks silly and offensive to assume one.
In any case, it is just cruel and dehumanizing to judge a real, specific person by a general tendency, even taking for granted that it exists in the first place (something I find exceedingly unlikely). People establish friendships and relationships with other people, not with their statistical likelihoods. Nor with their genders alone.