Watched a discovery channel special about how women, when close to ovulation, are way more likely to cheat than other times. They had women at different points of their cycles rating their attraction towards different men, including feminized or masculinized photos of the same guys. As they neared ovulation, they found the more 'manly' ones attractive, even if they were more attracted to the 'pretty' ones at other times.
From personal experience, women cheat all the time. People are flawed.
But yes, there are people out there who discriminate harshly against bi people. Guys who are 'bi' are gay and women who are 'bi' are attention whores, ask anybody!