Wow. I saw your post yesterday, but was too overwhelmed with various thoughts to put anything coherent down in writing. I'm still a little stumped, but would like to somehow offer my opinion... that is when I can narrow it down without sounding like I'm judging you. I don't want to do that.
I will say this: Staying for the sake of the children is a mistake... or, at least, it was in my parents' case. I'm still trying to overcome the poor relationship example my folks modeled for me.
YOU are responsible for your own happiness... your wife hers, your mistress, hers. Personally, I think you ought to figure out what you want and get off the fence. It's not fair to anyone involved for you to stay with a partner you no longer love. It's also not fair to jump into a new relationship (albiet an "old" one) while still struggling in a current one. Not fair to you, either.
I realize I'm all over the map here... I just know that, personally, being lied to about love sucks. I hope you can figure out what is true for you, and follow thru with it. Wouldn't it be nice to look back on this situation in the future and know that you did everything possible to keep your integrity intact?

If you feel like venting, or brainstorming, or want to discuss this anymore with me... don't hesitate to shoot me a pm.