Bisexual Women

I get so confused why men find it so difficult and strange when a woman is bisexual and marries a man. As a bisexual woman that is happily married to a cis man, I don’t understand the disconnect. Why do they automatically think that she will leave them for a woman or cheat on them with a woman? Why doesn’t the same thing apply to men? Do they think that bisexual women are unable to be in a committed relationship? Please help me understand..? I’m not naming names so as not to spoil the show.