Hey LB. Sorry to hear of your latest news - that really [censored].
I don't really know what to tell you, legal-wise. I would suggest speaking to a L before you decide anything.
In regards to yourself, I guess it all depends on if you've had enough. This is only speculation on my part, but I think that if you let them know what you know, it will have to be a reveal that has some action attached to it on your part, ie. "Since this is the action you have decided to take, I will be _______".
Of course, if you do nothing, there is always the possibility that your kids may reveal to your W that they told you. Either way, I would think about it and prepare yourself for a response so you aren't blindsided.
I guess the question becomes - are you willing to wait this out? Are you willing to keep standing?
It's not an easy position to be in, I feel for you, man.
Always remember what the old threads talk about so much. The OP is a symptom of the MLC. It means nothing. Never compare yourself to the OP. They can never "replace" you. And on some level, buried deep down, even if she never shows it or says it, your W knows that what she is doing is not ok.