First we had the conversation with Nicole and her sister, and then with her client about the open relationship.
The only thing definite we got from those, was Nicole was not going to cheat (there was nothing to say that she would not be interested in sex with someone else, especially after her comment about the threesome and the third person being a guy).
Then with the way that she raised the open relationship with the MC, I'm not sure how we were expected to think Nicole would not have had sex with anyone else.
Afterwards we were told (among the cryptic comments, troll posts and untruths) that Nicole was not going to have sex with anyone, but that was done as badly as the story itself, and by then, many people had already made their mind up.
As u said, in the scene with Gorgina she was clearly interested in meeting with other men, also as said before, why would she propose a open relationship if she didn't want to take advantage of that, especially as she and MC are effective on a break, being in different countys...it makes no sense.
Add to that the direction which DMD goes with open relationship/sharing, there was literally no reason to assume she would stay faithful....i don't really belive that it was never planed/in consideration that she wouldn't have sex with others, more likely a choice if we want to see it, maybe a choice to make it optional...
About the client and how a OR maybe could have saved the relaionship.
As far as i can tell, the MC isn't even aware of the fact that their relationship has serious problems, stress, some minor fights and him being a bit jealous of her being a lawyer in court sure, but not large problems which threaten their relationship.
So if Nicole suggest the OR to save their relationship, she probably should have talked with the MC about the problems first...instead of making a sleghammer solution, for which the MC doesn't even know the problem...
In the talk with the Sister MC said, he only agreed because it seems important to Nicole, it is clearly not something he is comfortable with, nothing he wanted and clearly not a solution for their problems in his eyes, instead it is likely the largest problem for him (at least problems he is aware of), seeing his reaction...