You shouldn't have agreed to it. Now that you have - you've got to deal with the situation as it exists.
This was part of the grounds for my suggested solution, on which I would like to elaborate a bit.
In this hypothetical <ahem> case, the husband agreed to the open marriage. So he can't simply go
backto the status quo ante of marital monogamy. When he tries to do that, the wife makes him the bad guy for going back on his agreement. His solution has to involve going
forward from under the new "contract" he made when he agreed to the open marriage. I'm trying to get him his marriage back, because that's what he wants, from under the paradigm of the open marriage.
The way to do
that it seems to me, is to use the very concept of the open marriage to put at risk for the wife something that she actually probably values more highly than hot sex with Mr. Muscle, namely, the marriage. She's not consciously aware that she values that more highly, because right now she doesn't have to be She just takes the marriage as a given (because the husband has made it one).
Here I'm going to draw on my go-to source for relationship advice, Amy Alkon, the Advice Goddess. She writes a newspaper column where she tackles issues like this all the time, and she always does so by invoking evolutionary biology. You know the principles. Men evolved to want mates with a high likelihood of producing offspring; women evolved to value men who will stay around and nurture the offspring; to do that, men want to know it's theirs, so men strongly value fidelity in their mates. These drives drive us more powerfully than more rational considerations.
This woman wants husband to keep paying the bills for wife and daughter. That, according to Alkon, is her most profound, irrationally-strong desire, and if she sees that at risk, she'll abandon any other interest. She doesn't see it as being at risk, so right now she feels she can have Mr. Muscle as well as Mr. Provider. (In fact, as one sign of men's dependibility as a provider, women like grandiose gifts, gifts that a man wouldn't give unless he meant to stay around. The wife is presently taking permission-to-have-sex-with-Mr-Muscle
as such a gift. On one level it's satisfying her even more with her husband. (Note I didn't say making her love him more).)
But the concept of the open marriage gives the opportunity to put what the woman most deeply craves at risk. He just says, "I'm glad you've opened our marriage. I'm going to use the freedom as the opportunity to look around for someone who will satisfy
me. What I'm satisfied with is marital fidelity. So if I find someone who will give me that, I'll be deeply satisfied. I hope it can be you. But if it can't be, I feel certain you'll understand if I divorce you to marry someone who can give me what I want. After all, it was you who suggested that we each be allowed to seek after what satisfies us."
Then, in her view, chat up a lot of women, as though you're interviewing them, but show special favor to one, look like you might be taking your dependibility off to one in particular.
