As a poly person, I have moments of separateness, when I'm alone with one love or another. I spend two nights a week with Mono. I live a separate life there. The difference is in how I treat my loves. I am present when I am with them, and if they call, I am present in that moment too. When we are together, I am present with them as a group. They all know each other and respect each other because we have been on a journey together whereby everyone has been respected. It has created safety and reassurance for them, I think, that no one of us will disrespect their needs. Everyone is looked after/taken care of (very East Coast Canada way of saying it) by the other.
I think, in an ideal world, it would be better to study the theory of poly long before actively being poly. Hopefully this site helps with that. Nora, bless her heart, fell for someone before really knowing what she was doing and how to create what she wanted and perhaps needed. It's unfortunate, as you, Dazed, have had to bear the brunt of her ignorance. It doesn't make her bad, but she has a lot of things to learn, and a lot of things to correct. It's going to be a huge undertaking, now that she has cheated, to achieve her goal, if, in fact, it is polyamory she seeks.
I hope she stays humble on that journey, is patient and allows a long time to heal herself, and respects that you need healing, too. As I said before, when I went through a similar situation, it took years for me to regain a friendship with my ex-wife. I have become a changed person because of that journey. It was worth every struggling moment.