She is placing her interest and desires above the best interest of the marriage. This is selfish and singluar thinking. Additionally if she does go through with it, you've lost power in the relationship. She will now view you as weak and not view you as someone able to be an equal with her. Perhaps she already feels this way, who knows.
Hate to say it..but there is no win in this. You know deep down you need to move on...you're just on the fence waiting for something to kick ya in that direction.
I feel for ya bud...you sound like a decent guy with decent expectations for a relationship. Where as many women today can't see a good thing right in front of them. They are too focused on whatever their desire of the hour is or their emotion of the hour.
You can talk logic all week long to a woman..it won't change a darn thing. They will always act out of emotion even if that puts them backwards in the long run.