I would like to point out that you have not agreed to polyship. You have agreed to TALK ABOUT polyshipping with these people.
I don't know that you'd want to enter into a relationship with broken trust and weak communication skills between you and wife. Sounds like shaky foundations to me right there and who knows what he brings to the table to add to the pile.
But in this week? Could assess each person's fitness for such a thing -- because even if all are WILLING? They may not all be ABLE, and may not all have the skills/resources required to sustain a healthy polyship.
He can stay in a hotel that week. So everyone has space to chill if they want to. And while all 3 are there together that week? At the very minimum? Could cover these together:
Better if you all slowed this WAY DOWN and read more. Here's some hub pages.
You'd have to look elsewhere for more on healing broken trust from an affair.
You know yourself best. But if you are not going into this with joy in your heart
but from a sense of "I am afraid to lose her if I don't do this" and riddled with doubts? It doesn't sound to me like you are looking out for your own well being as best as you could and like you are signing up for something fun for you.
Don't be afraid to ask point blank when you 3 talk -- "What's in this for me other than being in wife's orbit still? Does that mean wife is going to meet your wants, needs and limits now? Or still not meet them -- esp the trust breaking thing?"
If this were shopping for a car -- you'd want to know more. Gas mileage, cost, how many passengers it holds, good for city driving or country, etc. So... .take the week to REALLY kick the tires on this offer she is presenting you with. Get a sense of what you are buying into.
Right now the offer sounds flimsy to me. But you could take the week to assess.
I'd also like to point out -- you aren't "saving" the marriage from ending if you go there into trying out a polyship.
The 2 person marriage IS ending. Possible outcomes that I can see from here (There could be others I do not see):
It could be ending so it could become a healthy 3 person thing that healed from cheating start. The polyship happens and it goes well. (Good for your short term and long term health maybe)
It could be ending (as you knew it) and the polyship does not happen at all but in the talking about it you and wife gain new understanding of each other and rebuild a marriage after a cheating affair. (Good for your short term and long term health maybe)
It could be ending (as you knew it) and you have an experimental polyship for a time that folds. But you and wife grow from that experience and rebuild a stronger marriage. (some short term turbulence, but long term health ok for you maybe.)
It could be ending because she's no longer willing to uphold your previous boundaries/marriage agreements. In renegotiation and assessing polyship offer you find you no longer have matching wants/needs/limits/goals for a shared future. You could part cleanly first, and then go off to start new things with other people. (Not stellar for you short term, but good for you long term.)
It could be ending (as you knew it) and you have an experimental polyship for a time that folds. You and wife break up. (some short term turbulence, but long term health ok for you maybe.)
It could be ending the long slow torture way with potential to achieve big levels of stress and personal pain because you failed to talk/assess realistically at the beginning to weigh out the pros and cons. You all just jump in the new car you all buy. Stepped on the gas, covered eyes, and sit praying the car doesn't crash.... but who's steering and where is it even going? (Bad for your health short term and long term health to go live in Crazy Town because you don't want to talk about realistic healthy break ups instead.)
In all possible paths -- she and he will have the initial joys of being with new partner so she's on the upper track in this image for the emotional cycle of change
that will be felt by all three of you. They have that to sustain them through the uncomfortable period.
You are on the lower track. What will you have to sustain you that you will provide? What will you have to sustain you that each will provide? So you can come through the initial uncomfortable period? Could talk that out -- what the plan is to weather the transition time so ALL the players come out ok in the end of it? And if the plan sounds "meh" to you? Could not sign up to do this.
If you all can make it through and achieve success -- that's great. I'm not knocking it.
But I'm also not kidding you -- it's a hard road to travel even in best of circumstances. You guys are thinking about taking it on in poor circumstances
and you'd be well within your rights to say "After this week of serious thought? And contemplating your offer? And what changes to come that would all entail? And what emotional journey would have to be made? I'm sorry, but NO THANK YOU. I am not willing/able to participate in an offer like that. "
Then you could all come up with a new offer and a new set of agreements to consider or just agree this isn't gonna be a runner.
Tread carefully. You are responsible for your own well being first -- put your own oxygen mask on.
It's ok to be a Fool and step out into a new journey and go out to explore where you've never been before. But you don't have to do it by jumping off a cliff and you could try to go with a map and a compass at least.