Like others have said, you are VERY lucky you don't have kids with this woman. You can leave cleanly. You probably want to save the marriage in order to save your ego. You want your wife to choose you over this other guy. You want to win her back.
The more you try to save your marriage, the more desperate you will look. The more desperate you look, the more unattractive you will be to her anyway. Leave. It's not your responsibility to fix this mess.
Go to court and get a motion for a legal separation. The longer you stay legally married to this b#tch, the more alimony she gets. Filing for legal separation should put a monetary halt to your marriage.
Go to court and then the next time you see her, casually say "I went to see a lawyer today !" Show her the document.
This happens too much: A guy works his ass off only to lose his wife because she felt "bored", "unloved", "unappreciated". Never mind that the guy was working his ass off for a better life for both of them.
You will be amazed, simply amazed, at how women take their wife "duty" lightly, until it's time for them to get their money from their marriage. At that time, they become "100% your wife", because the wife, not the girlfriend, gets the divorce money.
I hate to say this bro, but she doesn't love you. You are in pain, and it's going to sting for a while. You have friends here that are giving their heartfelt advice. Your inner voice is saying that your situation's different. That this marriage can be saved. Your wife had the chance to save it before it came down to you writing your story here. She didn't.
This is an opportunity for you that is diguising itself as something negative. You only live once. Do you want to be with her ten years from now, with this crap still tormenting you ? Or do you want to be proud of yourself for standing up for yourself ?