So, I'm a young fellow, currently in a committed relationship, but in the past I've been in open ones, polyamorous ones, casual ones... I've had my share of sex/love things where another person gets involved, is what I'm saying. The one rule I've had that entire time is never cheat; it does nobody any good. Not you, not your wife, not the new girl... yes, you'll get a thrill, yes there will be fun times, but eventually those chickens come home to roost.
Now, the naive part of me wants to suggest trying poly stuff for yourself, but I know most people aren't set up for that.
Ultimately, if it was me it'd be down to two choices: stay with the one you're with, or leave for the new pasture. I wouldn't encourage you one way or the other- you're the only one in your headspace, it's your call to make- but I wouldn't consider cheating as an option; even if you do get away with it forever, you'll still know. You seem like a pretty good guy, I doubt you'd feel completely okay with it.
That being said, there's nothing wrong with having these feelings, nor with expressing them, and I reserve the right to just be completely wrong here on every point.
All's I can do is wish you luck in the end, and hope that whatever decision you do make, it's the right one.
Now, the naive part of me wants to suggest trying poly stuff for yourself, but I know most people aren't set up for that.

That being said, there's nothing wrong with having these feelings, nor with expressing them, and I reserve the right to just be completely wrong here on every point.

"YOU take the hard look in the mirror. You are everything that is wrong with this world. The only thing important to you, is you." - ronedee
Want to see more of my writing? Check out my (safe for work!) site, Unprotected Sects!
Want to see more of my writing? Check out my (safe for work!) site, Unprotected Sects!