Well, as they say, been there, done that. Attraction is a funny thing. Want what we can't have and the grass is always greener. Loved the line about "he'll never hurt me" referring to the OM. Those are the words spoken most likely in the middle of romantic love where the SO can do no wrong and you can do no right.
Right now it is all about her and she justifies it because she was "ignored" for so long. It just sounds like her interests are elsewhere.
You can chose to hang in there for family, history, etc., but while she is "elsewhere", but make sure you take care of yourself. What I mean by that is find yourself a safe place away from the confusion....your own place if you can. Go on some dates...just doing that helped me realize that I was not such a bad person and deserved to be treated well. Your wife will not be right for a really long time. If she loves her OM, then if she decides to leave him, there will be a long period of depression because of the loss as she hopefully will decide to come back to you....to the place that at one time was full of pain and neglect....but that all can be overcome....but it will take more time and work than you ever thought possible. But, provided that you are the new amazing spouse, one day, things will be better. They will be totally different as you can never be the way you were again because if you are, then you will trigger all her negative feelings about you and the marriage.
But one day, you will feel the ship change directions. It will be very subtle at first as she tests the waters. Play along, be a friend. In the back of her mind she probably wants it to work for the same reasons you do, but it just won't be on your schedule. She will test you and frustrate you....be kind, gentle, supportive, yet unavailable at times. Don't always answer your cell phone. Be busy sometimes. Let her miss you a little, but just a little.
I have spoken enough for now. Your plight was mine...it started in 2002 and is finally ending but will still have a ways to go with a totally new relationship.