Whether you realize it or not--your actions are going to profoundly effect everyone--your kids included.
I think--before you do anything you should read "When love dies - how to save a hopeless marraige" by Judy Bodmer
And***** you should go and see a family therapist (by yourself) who will explain to you that your feelings are anything but unique. That your temporary rush for this new person will fade because is chemicals and hormones created by nature and meant to aid in procreation. That your new realtionship will eventually loose that burst you're high on--because real life will sink in after the secret is out--there will still be life and problems to deal with. That your new lover will not trust and respect you--because the stats don't lie. That relationships started in deciet sow massive seeds of distrust--on both sides. Will she trust you in the long run? And--will you trust her? How seriously does she take marriage? If she is running around with someone else's husband--you can bet she doesn't take it too seriously. And are you comparing her to your wife? Do you know this is a classic form of rationalization, one that proceeds to all sorts of character breakdowns? I mean really--if you spent your time working on putting the spark back in your marraige instead of convincing yourself that you are a victim and this new lady is your rescuer--well, I think you'd be better off.
I've been in your shoes. Don't wake up where I did. If you do--you're gonna be lost and far from home. And it will take much more work to get back home than it will fix this mess now. And by fixing it--I mean growing up and understanding that love is about much more than your grion and how good this new gal makes you feel (did you know this is chemical too--a hormone released in the beginning of all new realtiionships, especially secret ones--and some scientists say it's as adictive as morphine?). Love is all about putting someone else's needs above your own--BECAUSE YOU CARE ABOUT THEM. Seeking pleasure despite the costs--to your children if no one else--IS NOT LOVE, IT IS LUST. Love is a behavior, not just an emotion. Lust will trick you--it will decieve you--it will cheat you.
Believe it or not--this is all written in good will. But it's something you need to read.