I have a methodology that has been successful for many in dealing with comparable situations like you are in...
First of all: What is it you fear the most from what you discovered? Is that losing your wife? Turns out that for many men, that is what they see as the worst outcome – that their wife leaves with OM and their marriage ends in a burning wreck. Well... If THAT is your greatest fear then I suggest you allow your wife to have her affair. Learn how to turn a blind eye when she says she’s going "out" and take regular STD tests. Statistically infidelity-based relationships seldom last more than 18 months, so odds are you only have a year and a half left...
If that doesn’t sound too good...
What is it you fear the most?
I think the absolute worst outcome might be thinking things were OK, maybe even doing all the work to reconcile, to communicate, to be more attentive and all that... and then maybe 8 months from now discovering she’s still seeing OM.
SHARING your wife is definitely worse than LOSING her!
I also get that a 20 year marriage and three kids is something you would want to save. Only keep in mind that our collective experience here has strongly supported a number of behaviors. I don’t call them facts because there are few absolutes in human behavior:
A marriage can only reconcile if the truth is on the table. Like – if your wife was seeing him for 5 months and they had sex 273 times then the three-months-three-times will come back to haunt you both. Knowing NOW that it was 273 times will do less damage than learning 3-4 months from now that it was 5 times and not 3. YOU NEED THE ABSOLUTE TRUTH TO RECONCILE.
The affair is totally 100% on her. Your lack of attention or affection or whatever is NEVER going to explain or justify her decision to have an affair. If the marriage was lacking then it’s up to her to point it out and demand change. That change could be divorce, but NEVER another lover.
I venture that in 99% of instances the affair is about validation. A low self-worth. A false need for some verification. We all need verification, but while you might get yours through a pay-raise for a good job or by waxing your brand-new paid for Mustang she got it through the courting and desire of another man. This is why IC is a must for her.
Part of the truth is knowing who OM is, and if he’s married. If married you tell his wife – without any warning to OM or your wife. Our experience suggests that if you don’t do this then within six months there is something like a 70% chance the OM will be sniffing around again. Fishing for a chance to learn how you reacted and what you did. Since you haven’t told his wife he’s willing to risk it to get some tail. There is a 50% chance that your wife will fall for it... Maybe only to have a coffee to get closure, but that closure tends to end with both along in a car doing weird stuff...
At the same time in about 90% of instances where the OM wife is told, the OM closes 100% on the WW. Being turned down by the White Prince of her fantasy tends to be a real mood-killer.
With all this in mind then this is what I suggest:
Tell your wife she’s free to go be with OM.
Tell her that if you are so impossible, unimaginative, unatentive, uninteresting or whatever made her decide she had to go find happiness with another man then that’ fine. It’s not what you wanted, now how you envisioned your life, but it beats being there because she feels she has no options. You love her too much to want to hold back on her happiness and to keep her chained. You sett her free. Only... not as your wife.
Tell her that you absolve her of any expectations you could expect as her husband. Ask that she be considerate and maybe not date OM too blatantly and definitely keep him out of the house. But she can go be with him, spend time with him, sleep over... whatever. You no longer have any expectations of her as your wife.
This is not what you want, but it beats sharing her or having to experience that she wants to be elsewhere.
Let her know that there is a fair process to dissolve a marriage. You won’t make it harder than it need be. It will definitely impact your lives, and the lives of the kids, but it beats having them live in what is essentially a gilded prison. The kids or finances are NOT a valid or good reason to remain married. Neither were there when you committed to each other.
Tell her that if this is not what she wants she needs to let you know very clearly that she wants this marriage. She also needs to know there are some requirements she needs to meet: Total accountability, a verifiable truth, a commitment to IC and later on MC (to name a few).
Let her know that you will start the process, and suggest she educate herself on how best to go through this. Tell her a priority will be to let the kids know, but that can wait until you have decided on how and when you will finalize the broad details.
Then go make a sandwich. Watch TV. Whatever. You have said you piece and are content because YOU are getting out of infidelity. You aren’t feeding her romance by chasing after her, you aren’t accepting having "forced" her to cheat, nor having removed her "eternal soul-mate" from her life. Once she has the freedom... they tend to realize that what they thought they wanted isn’t what they want.
If she wants to talk about relationship issues: I’m sorry but this isn’t relevant. We are only husband and wife in name and we are working at getting out of that. If we were working on the marriage this might be something to look into, but while you are committed to your infidelity there isn’t any need.
Yes – You ARE committed to your infidelity while you don’t tell me you want us, and while you keep secrets from me, showing you are thinking more of yourself and him than us.
Friend – the above sounds harsh... but I have had the same approach for several years, and over those years I have gotten feedback from many that have followed the advice and have managed to move on out from infidelity. Most through reconciliation, but many by eventual divorce. What the later group tends to agree on is that it was inevitable, not necessarily because they wanted it but because the WS really had no intention to stop. In both cases – R or D – it beats being where you are right now.