I've been married 11 years. I had an affair off/on for many of those-with GG.
I came out as poly a year ago.
I only say that-to reference my perspective in what I'm about to say.
Your husband is being an ass.
Can it work? Yes.
But first you need to fix what is wrong.
You can't build a mansion on top of a rotting house that has a faulty foundation.
Can it work with the three of you? Possibly.
But-you still can't make that happen until you fix the problems.
If she's "possibly going to move on" then it wasn't meant to be.
GG and I have been friends for 17 years.
When all hell broke loose and the affair came out in the open, we didn't see each other for over 6 months. Our contact was limited even by mail/email/phone. Because there was NOTHING we could do until the HORROR that was the aftermath of me breaking Maca's heart was dealt with.
There is no way you can move forward first. That's a disaster waiting to happen.
I tried my best-as the cheater-to give Maca time, freedom, whatever before moving forward.
He lied to himself (not intentionally) and here we are struggling because he found that he wasn't healed enough to deal with moving forward.
So 5 kids at home, he's living elsewhere trying to deal with his emotions.
TAKE TIME TO BE SURE YOU ARE IN A HEALTHY PLACE FOR YOURSELF before EVER adding a new person to your dynamic.
"Love As Thou Wilt"