I think I know how you are feeling about protecting your W from public humiliation, but if you've read any of the threads in the infidelity forum you will know that "exposure" is the best way to shine light into the secret affair.
Protecting your W from the consequences of her sin is not what you need to do. Trust me when I tell you that I did not always think that! But, I thought like the WAW that I was and I knew I didn't want anyone to know what I had done.
Your W is playing you and she has all this time. Now, she is making you feel that it is your job as her H to protect her "good name"? Pl.....ease! Well, I thought that too, but was I ever wrong! When the secret is exposed, then the fantasy is shot to hell and that pretty much puts a damper on the A. So, think about it.
The best thing you can do for your M is to let the stuff hit the public fan. You are scared to death.....and she knows it. You are scared to death....not for her exposure,but that she will run to OM. She treats you like a child, patting your head and telling you to "believe" her when she says she loves you.
Let me ask you something.....can you stop her and the OM "if" they chose to run off together? No, you can't. Is you M anymore dead today while she's having an A with him than it was several months ago when she was having the same A with the same man? Nope. What has changed? You didn't, she didn't and neither did OM. The only one who showed any courage was the OM's W and now you want her to keep silent???
That is not strength on your part, sir, that is being a coward. Your W won't tell you, so I will......she has wanted to see you act like a man for so many years, but you apparently forgot how to do that. I can tell you that she will not respect you for helping her keep her secret, she will think you are a fool to help her. Oh you can expect a lot of drama from her b/c that is how she gets her way and controls you, but what do you have to lose? You've already lost her emotionally and respectfully. This MR is already dead. You do have a shot at winning her respect and having a new MR with her......but it won't be through "talking"her to death. It will be with action....."your" action.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!