There is always choice. You face some now.
While I am glad that you are not angry at how your life turned out, I am disturbed by your attitude and resentment toward wife. Dragging things up from the past is not helpful. Even if you still need to lay them to rest appropriately? It's mixing apples and oranges.
Rather than dump that at her -- because she's now the mother of your child AND the woman you want to forgive an affair and enter into polyship -- you could secure another counselor to sort that out on your own if your current one is not helping. Guard against using that as a "guilt trip card" to get what you want with the polyship thing.
A divorce might serve you if you still feel that deep of resentment and like your life "got postponed" or something. Even if you are not angry about how that life turned out. While it entails short term break up feelings that affects your short term health (ex: stress), it could lead to long term health improvements for all.
Could help you let go of resentment, maybe freedom from cheating affair for all, and for wife? Maybe puts you all on equal footing if she is financially dependent and just going along with it because of that. Puts you and U on equal psychological footing because then wife can't hold "do x or divorce!" over your heads. Not saying any of you would use unfair cards, but making them non-issues
is something to think about.
Could think the "divorce option" all the way through and list pros/cons. A serious evaluation with your wife... AND U. She doesn't have any say in the marriage staying together or not, but she could have feelings/fears to air about about the state of the marital union and it's impact on the potential polyship.
If your wife is going through the stages of grief,
could read on that. And examine polyhell
article together. Maybe secure a separate grief counselor for her?
This one describe one way to open a formerly monogamous relationship.
Maybe it could help when you are ready to move on that.
But I don't suggest rushing into polyship here -- imagine together what that might be, sure. But the FIRST main focus could be healing all these old hurts (resentment) and new hurts (affair) and as yet unknown hurts (does U have any?) so that all players are healthy and WELL before entering into a new thing. It could be a time for Radical Honesty now.
Polyshipping is intense and can result in magnifying ALL previous cracks. Could not Open when Broken. Could get solid first in preparation.
Could also talk about the plan for what happens if after all this consideration and preparation it is still just not a runner. Neither of these women is obligated to go along with it. So back at that square -- do the breaking up talks. Whether it is break up with U, the wife, or both.
Do the W's and H' as deep as possible to assess you, wife and U's fitness for this.
- WHO is polyshipping? How does this affect polyship success?
- WHAT is the plan? How does this affect polyship success?
- WHEN are we polyshipping? How does this affect polyship success?
- WHERE are we polyshipping?How does this affect polyship success?
- HOW are we going to polyshipping? How does this affect polyship success?
- WHY are we polyshipping? How does this affect polyship success?
Or go through the whole pre-marriage lists/courses an change "marriage" to "3 person polyship" and assess your collective fitness for this that way.
You already had a sloppy start to polyshipping potential with the cheating affair. Not at the actual polyshipping yet. But could guard against more sloppy beginnings and sloppy endings.
You have opportunity to make NEW choices here. Choose well.