Trumpet, you have to detach now. I know you thought you were, but you absolutely must get far from her emotionally. She is going to destroy the life you two built, and you can't be anywhere near ground zero. You said she needs help, but my challenge is always "how can you expect her to let go of OM if you can't let go of her"?
Of course she is in an EA/PA. Of course her friends are jumping on the bandwagon. Of course no one sees it your way, you can't blame your kids for believing what they wished was true, shoot, even you said you were almost doing that. And yes, the world is how it is, and most people consider divorce a natural progression in this 'get yours' world.
It hurts. It stinks. We see it all over, but somehow we think we're different, our love is special, it won't happen to us. Unfortunately our culture is twisted and this is the new normal. And because of that the odds of this somehow turning around are slim. I'm not telling you not to stand for your marriage, but hope will not serve you here, not if it means being unprepared for the reality.
Be sad. Be pissed off. Be jaded. Be bitter. Be whatever you need to be...but then calm down and take care of yourself. All of the stuff you talked about doesn't matter. What matters is what you believe, what you do. Live in a way so that if you're divorced in 3-6 months and she's remarried you won't have any regrets with how you played your cards.
Sorry you're here. There's nowhere worse. More than ever it's time to lean on God and be stubbornly appreciative for whatever you have left to celebrate.
Me:38 XW:38 T:11 years M:8 years Kids: S14, D11, D7 BD/Move out day: 6/17/14, D final Dec 15