Why do women get upset with other women when they talk to their men?

I will never understand why do many women get mad at other women that talk/flirt with their men. If my husband was talking/flirting I'd be mad at him not the other women. I have a friend that gets do mad when her SO talks to other women, which I understand but she doesn't get mad at him she gets mad at the girls he talks too. Am I the only women that holds there man accountable of his actions. If you get mad at the other women help me understand why?