Pure Gold from Wk55hn, this should be a stickie.
Some people are fucked up with their ideas about romantic "love." Men can be really screwed up. Women too, but the sexes are different. I grew up in a big family, had two sisters, pretty close, bedroom was next to mine. I am about 50, over the years I've seen that some of the shit they've come out with them and their friends, it's the same crap I heard them talk about when they were 12. Happily ever after, Prince Charming, destiny, soulmates. I don't know about you, but as I grew up, I looked around at older people, my parents, parents of my friends, uncles and aunts and in-laws, and I never met Prince Charming. Those long-term marriages were happy enough, contented, satisfied, indifferent, too-lazy-to-change - all kinds of marriages - but "happily ever after," "madly and passionately in love" - not a single one.
One of my friends a few years back tells me, "I'm divorcing, I haven't been happy for years." I told him "what the hell does 'happy' have to do with it? I know your parents, they married 30-something years, I'm pretty sure they weren't 'happy.' My parents weren't 'happy.' They loved each other, but not 'happy' like you think 'happy.' What's up, you been cheating?" And sure enough, that's what it was. He refused to give up the other woman, his wife divorced him, and the other woman left very shortly after she got him full-time - who knew? She only liked being taken on dates and told how hot she was, she didn't want to deal with all his shit.
So your wife? I think she doesn't have a clue. I think she has some childish fantasy-type ideas about real life. Dude, she's in love with another guy. She's been with you 14 frigging years, she met this other jackass a few months ago. And somehow she can't choose between you and him? Are you kidding me? Fuck her. Let her go be mommy to that jerk and his two little offspring. See how that works out for her.
And you? You've been enabling her. Waiting for her to choose. Again, are you kidding me? You are a successful young guy, do you know the value of a guy like you on the dating scene? Loyal? Able to commit? Reliable, successful, NORMAL? Women your age can't find guys like that too easy.
When I found out, I confronted my wife as soon as the kids were in bed, and I told her if she is so "in love" with other man, she should be with him, as a matter of fact, let's start packing, I'll help, I'll give him a call, he wins, and I'll be sending you over to him shortly. I was so damn angry. I hope you finally found your anger.
When you confront her, tell her that she has complete control of herself, and you don't want to control her. But you can control yourself, too, and you don't want to be in a 3-way relationship. It is unacceptable to you. You would be willing to work on the marriage in good faith, if she did, but in no way if there is a third person in the marriage. UNACCEPTABLE. You will work on the marriage if she drops the other man and gives you evidence that she has ended it, otherwise you are moving forward. You will not tell her what you plan to do, but it might include divorce, and you will do whatever you want to do when you are ready to do it. You make no promise that you will be willing to work on the marriage in the future. Your feelings are changing up and down every day, and you might decide you don't want to bother if she pushes you further.
Tell her you don't care if she calls it an "affair" or a "friendship" or a "flirtation" or whatever the hell she wants to call it, it is UNACCEPTABLE.
Do not give any ultimatums, let her know you are moving on, then distance yourself from her, detach, be polite, but do not talk with her of your relationship, the future, nothing but mundane chores, finances, or small talk, nice weather, isn't it. Be as happy as you can. If you can't detach, if you can't stay with her unless you are angry or sad, then stay out of the house more, come in late, go to bed, then go to work. If she wants to talk with you about the relationship, ask her if she did what you asked - drop him and give you evidence. If no, then tell her, "I have nothing to say. I refuse to be in a marriage with three people."
If you file and get her served, great. It takes a while to go through that process, and you can take her back if you decide. If you can't force yourself to file, fine, just get distant and detach. You will file when you are ready.
Even if she agrees to ending the affair, but she works with him, so that is really problematic. But you can cross that bridge if you ever arrive at that situation.