I've always thought the idea of bisexual partners being more threatening "because they have twice as many people to cheat with" is ridiculous. That says something about their MORALS, not their SEXUALITY (of course, some people will argue being bisexual is immoral... but that's another issue). If someone is going to cheat on you, it's not a matter of numbers - it's a matter of opportunity. Heterosexual, homosexual, bisexual, etc. partners cheat because they don't respect their partners, because they choose not to communicate with their partners when dissatisfied with their relationship, because they're afraid of the intimacy/commitment, and so on.