Yulia, in my opinion the guilt or shame comes from growing up in cultures where monogamy is deeply ingrained. We've all been sold the myths around "one true love" etc. As I quoted in the OP, one expert commented that “We are deeply programmed for monogamy and even when we choose to practice otherwise, the impulses and feelings we get don’t follow suit so quickly."

It really truly does take a type of deprogramming in order to fully embrace any sort of ethical non-monogamy. There are several very good books out there which can help with that. My favorite is Opening Up by Tristan Taormino. It does a great job of posing questions for people to consider and for partners to discuss as they go on this journey - and it very much is a journey into a very different relationship style. And, that being said, the work is ongoing to face fears, jealousy, etc. You have to be committed to continuing to do your own work and to having on-going high level communication with anyone else involved.

I'm a firm believer in spending weeks if not months thinking about these things and having these conversations, before ever contemplating becoming involved with anyone else. One of the things that can end up really bringing existing couples together in this is to begin practicing this deep level of vulnerability with each other. I mentioned in another story that my husband and I spent a long time telling each other things that we would have never dared say to each other under the umbrella of monogamous marriage before we ever saw anyone else. We talked about attractions we'd had to other people, fantasies we'd never spoken before, and things like that. By the time we were with other people, he and I were very clear in our deep connection to each other but also very clear about what we wanted out of opening up.

I'd also like to add that people who are very insecure to begin with, or very prone to co-dependent or controlling behaviors may not be good candidates for ENM. It's easier to make the transition when you aren't starting with a lot of that in the first place. I hope that helps.