Just adding a bit of my story where it is relevant to this thread...
I was married for 15 years when I fell in love with someone else as well. My relationship with my wife at the time was going amazingly well and I unintentionally fell for someone else as well. That was 7 years ago.
I knew nothing about polyamory at the time and was involved in a Christian church (I was actually the pastor - lol!). I thought falling in love with someone else was not supposed to happen - but I also felt it was OK and the right thing to do! I was honest with my wife about it and while she had alot of doubts about it being OK too, she tried to be OK with it.
After about 9 months of struggling with it, my wife finally pulled the pin and said she was not OK. She forced an abrupt ending to the other relationship. I loved both people dearly, and could also understand my wife not being OK with another relationship - especially because of the background we came out of. So reluctantly I agreed with my wife.
4 years later I stumbled across "polyamory" and it answered alot of questions for me. I shared my findings with my wife and she was like, "No way!". We continued journeying slowly. It was getting more and more clear for me that this was who I am, and that having multiple intimate relationships was how I wanted to live my life. My wife was still dead against it. We talked lots and lots and lots and were very open.
After much journeying, and the desire for multiple relationships getting even stronger for me, my wife could tell that we were going to reach a point where either we separated so that I could be me, or that she become OK with things. She felt that the only way that she could become OK with poly was if she found another relationship for herself. So internally she reached a point where she wanted to experience another relationship while still being married to me because she didn't want to separate.
Within weeks of reaching that internal decision she met someone else and has fallen in love within weeks! They are 2 months into their relationship now and she is really, really happy! It has been difficult for me, being the one to stick it out for nearly 7 years and ironically being the one not to have another love in my life, but this is all part of the journey. Unfortunately the other woman that I fell in love with has now moved on, so I am still finding that I am having to let go of the last remnants of grief and letting go process.
So overall it seems like after years of struggle we are reaching (have reached??) a place where my wife and I are now poly together and when the time is right I may even find another love...
I don't know how much of this journey is relevant to this thread, but I hope it helps...