While ENM doesn't always lead to affairs and cheating, it can do.
I agreed to open a relationship early on, lots of reasons, I didn't want to have sex outside of the relationship, nor was I interested in swinging either but accepted there were reasons why he did. It was discussed ad infinitum and agreements made. We were both confident, easy going people, who accepted that you can't control people, or so we thought.
Didn't make it past the month trial period before the jealousy started, his not mine. I had not been unfaithful in any way but he couldn't accept that he had several partners to explore with and I hadn't. It drove him to distraction, his grief was palpable and yet nothing had happened between me and any male passing within 10ft of me but the accusations were very real.
All ended up being very cruel, unaccepting, and controlling, and after he came home with yet another declaration of having found love with another woman, and he'd broken all the rules he'd set in place once again, I took him at his word and set him free to love as he pleased.
Absolutely not what he wanted at all and he was furious for years with me for allowing it to happen. 🙄 Had I realised the emotional damage it would do to us both, I'd have kissed him goodbye the moment the idea was mentioned and lived with the mild regret of not being kool enough. I definitely wouldn't do it again
So admittedly I'm biased, but there is nothing evolved about it, it is just a situation like any other that a couple agrees to. If it works for a relationship then that's fabulous but I wouldn't guarantee it will always work as a way to prevent cheating. It really doesn't and it brings to the surface emotions we don't always realise we have until it happens.
I don't care that people are using it as the old No Strings phrase, I'd just thank them for allowing to to avoid that shit show.