Polyamory anyone?

Was just reading a blog about a woman who is, and in the comments came to find that apparently it's pretty common! She herself was not married but, was dating tons of her friends husbands, yes, it includes sex, and her friends approval to "date" the husband! She said it was the best option for her because she didn't want to get married and didn't want the pressure of having kids so dating her friends husbands worked well 😳 I'm just trying to grasp the concept of it all because there is no way in hell I would ever be ok with another woman seeing my husband in any way shape or form, how do they combat jealousy?!