I'm Isaac, and I'm the husband.
She put it perfectly, which is why I am not starting my own thread.
In answer to sage on the emotions side of it, it's definitely new. But I haven't felt negative emotions. Dealing with the side of me that would have had problems with this because of my past has allowed me to move on from that past in ways I had never really quite accomplished. In this way, just the conversation about polyamory being so open has helped me change a lot of worldviews that needed tweaking.
I say all of that to say that this was never a matter of me allowing her to do something based only on logic, it holds a lot of possibilities for freedom from other things for me, things I have needed to let go of for far too long now.