ppenton, sorry about your situation. Unfortunately though, the circumstances you find yourself in aren't unique. I don't mean to diminish it for you, but I want you to know many on here understand what your going through and what you will go through.
I know it seems like your whole world is unraveling right now, but there will be peace for you in the future regardless of the outcome. Believe that first and foremost as you formulate your plans.
Right now the newness of her relationship with this OM is what is so attractive to Her. Same excitement we get out of buying a new car or moving into a new house. It's hard wired into our brain. We love breaking the routine and experiencing new things. It stimulates us. I'm sure he's telling her everything she wants to hear right now. Don't take this personal. This OM has nothing on you. She's unable or unwilling to see that right now. Just the fact this OM will pursue a married woman gives you a little insight into his integrity. What kind of Man or Woman for that matter pursues a married person when there are so many singles to choose from? It's usually a desperate one with self respect issues. It will eventually surface for your W to see, It always does it seems. Statistics for relationships or marriages started after an affair don't bode well for them. You need to counter with strength of character. That means remaining calm, cool, and collected. Your priority has to be you and the kids for right now. Let her go!
"It is curious that physical courage should be so common in the world and moral courage so rare." -Mark Twain