Kris, it is okay to break down. We all do, even the toughest guys do. You either break down outside or break down inside, which is worse. You've been through an experience that people say, including me, is even worse than cancer. So don't worry about that, your reactions are normal, healthy and to be expected. Don't add to your own sorrow by giving yourself problems. There is no right way to respond to this because infidelity, which is betrayal, kicks all the slats out. It's kicks out the foundations of life. How are we supposed to respond to this?
Your wife is a long term problem. As she does not seem to be willing to end this or you can't yet receive any sense that she will, I would go to a lawyer and discuss divorce. Personally I would start the filing process because something definite needs to happen here. I think people have to take a stand on this issue of what their marriage will and won't be. What the boundaries are. When you see someone who wants to continue an affair, I think people need to set immediate and solid boundaries - I won't take this. This might very well shock her back into reality with all she might lose. And if she still won't stop, then you have no control over the situation, you can only decide what YOU want to do. One thing I will say is I don't think anyone should ever love someone else more than they love themselves. You've got to love and take care of yourself first....you come into life alone, except for Mom, and we all go out alone. Spouse is not gonna be in that coffin with us. These are all voluntary arrangements. You can't love someone else MORE than you love yourself, you can't put them on a pedestal. I think people need to take their spouses OFF the pedestals and be wiling to say, I'm going to leave you flat if this does not end NOW. And then they make their choice whatever it is. But the longer you stay in limbo, the longer this continues. And even if it stops with this affair partner, the problem has not been addressed, and they can just pick up later on with someone else. There is a problem with the spouse that they have to handle. THIS IS NOT YOUR FAULT. Even if they were unhappy in the marriage or unhappy with themselves, THIS is not the way to handle it because it is destructive to you AND the marriage without your knowledge. This destroys trust which may never come back (it didn't for me). You can only make your own lines in the sand. Now even if you start a divorce, you can always pull back from it up to the end, but it shows you're serious and you're willing to take an absolute stand of what you will and will not tolerate. People don't like to hear this I know but....I think it's the truth and I have to share it. You'll get all kinds of advice and support here, please stay with us no matter what you decide. I think it WILL help you.
As for your daughters, try not to be too hard on them as much as it hurts because....IMO, they didn't know what to do. They love you both, you're the house they grew up in - not the physical but emotional house. They don't want you to break up, they don't want either of you hurt, and they don't know what to do. They were afraid of hurting both of you by saying anything. This is so common. They were probably hoping this would blow over with Mom and that you'd never know. That sounds awful to hear but it's such a common hope people mistakenly have. Also, I don't know their ages, but it might also be above their maturity level to handle right now. So, keep the lines of communication open with them and talk to them about it, try to understand why they didn't tell you, and let them KNOW how you feel about this, how hurt and betrayed you feel. I think it's important that they know this. If you can't tell them one on one, maybe with a counselor present. But I think you 3 have to be honest with each other (2 daughters right?) because this will poison your future relationship if you all don't learn to understand each other. As hurt and angry as you are, please be willing to talk this out with them and also let them know it makes you distrust them too as it seems like they were more invested in protecting Mom's secret. They have to learn to handle things in their own future relationships too. I think your relationship with them is salvageable. Your wife, I just don't know, I tend to think when someone actively cheats that's about as big an obstacle to continuing marriage as I can think of as it really kind of states what they think of you and the marriage, and that there's no trust. It really is like throwing a grenade into the marriage. I would draw your line firmly in the sand and file for divorce. There is a reason why even the Bible allows for divorce because of adultery because adultery has traditionally been seen, to me, rightfully so, as the end of marriage. Maybe a new one can be started eventually....but this IS the end of the existing marriage. This behavior is NOT acceptable in marriage and has to end immediately. You can't control her or anyone, but you can make your own boundaries known and firm. Stand up for yourself. And don't accept ANY BLAME FOR THIS AT ALL. There is no excuse for adultery. There just isn't. It IS throwing a grenade into the marriage, you can't control the damage, you can't undo it, it is what it is....when someone does this, they are stating, to me, what they think of the marriage and what they think of their spouse. DON'T BLAME YOURSELF OR ACCEPT BLAME FROM HER because often when caught, they will try to twist it back on the spouse. And they will lie endlessly so you have to expect the worst and stand up firmly for yourself. LOVE YOU MORE THAN YOU LOVE HER.