If you had come into the relationship with the understanding that you'd both date/have sex with other people then great; it doesn't matter what other people think. However, when you say that it was hard for you to accept her being with other men, and that you're lucky that "she has never fallen in love and wanted to run away with one of em", damn. My first instinct is that you should take your own advice: find or design a relationship where you don't have to accept this.

I realize that some of my knee jerk reaction might just be instinct/cultural values, I mean no disrespect.

In experiments they have found that women are much more ok with sexual infidelity than men. They aren’t fully ok with it just more ok with it than men by a huge margin. There’s a huge gender difference and given how culture doesn’t differentiate this aspect in terms of teaching, logically the only origin is biological.

It fits with evolutionary psychology as well. If a wife engages in sexual infidelity a man could end up raising a child that is not his own and that is a huge evolutionary cost so men evolved to be extremely guarded against sexual affairs while for women the cost is just a man potentially raising another child. She loses resources of the man but if the man doesn’t raise another child it’s not as huge of a deal. This isn’t stuff I’m making up… it’s academic.

https://www.sciencedaily.com/releases/2015/10/151008083755.h...

For you to be in a polyamorous relationship you are definitely overriding your default biological drive and giving evolutionary advantages to your mate (if she is female and you male). Birth control largely eliminates this cost but the emotional states are the same in the sense that is a form of submission. Case in point: Most likely it is the female partner that initiated polyamory and the male partner who had to learn how to accept it.