There is nothing to explain. If she's willing to break her marital vows by inviting a predatory third party into her life, ending the partnership that god gave the two of you to cherish, and destroying a family...I don't think telling her "this isn't fair" is going to turn her around.
You mentioned a lot of what she said during the conversation. Starsky has a lot of good talking points about 'truth darts', I think it would've been a good idea to basically tell her that's what she was doing, and that she could twist things and point blame on you, but she was 100% accountable for her choices and they were destroying a family and nothing you wanted any part of.
But that window is closed. The only question that matters at this moment is what you are going to do. How as a man are you going to respond to this threat to your family. You can't save the M, but you can protect yourself and your children.
And you have to accept that it's unlikely that she'll ever feel she was wrong on this one. When the day comes you can stop having imaginary conversations trying to make her understand you'll know you are well on your way to detachment.
Be strong and take care of yourself U.
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