It's so great to have open relationships with not-jealous partner. But, unfortunately, remnants of stupid perception that woman's body "belongs" to her male partner, and if he "share" her with other ("Share"! What a word - as if she really belongs him!), it's a sign of weakness and a big shame (OMG LOL) is still alive in our society. So man's "pride" together with a jealousy prevents many men from having such a type of relationships (even if they possibly could like it, since if would allow them more freedom, too - if they wouldn't have prejudices). So most people will never understand, how good it feels to be free and sincere and don't feel guilty about the sex with whoever. ¯_(ツ)_/¯
Women, who are truly monogamous (i.e. feel comfortable with keeping physical fidelity for a long time), are very lucky. They live as they want, without a negative reaction from anybody. But women, who don't fall in this category (and I suppose that there are a lot of them), are usually induced to either cheat on their partner underhand (but this unethical behaviour may hurt relationships a lot, making them insincere and killing the trust) or constantly repress their sexuality and feel suppressed because of this (but, believe me, this can be a really huge stress factor, especially in the long run). So in this case having understanding partner is immeasurable.