Of course you should feel badly towards her, she has betrayed you every bit as much as he has.
There is no way on earth he can ever spin this to be something that just happened and is understandable and of course how could they have acted otherwise?
You don't let yourself develop feelings for your spouse's friends. And if you sense them developing you don't even consider acting on them.
What on earth gave this pair of reprobates the idea that them having a relationship was permissable? Even if they felt they were star-crossed lovers, destined to be together, they still should have denied themselves because of the horrible pain they were going to cause people they were supposed to love.
Instead they put their selfish bastard selves first and you and your children nowhere.
It is actually sickening that he is giving you all this guff about how the children love this woman. No they fucking well don't. They thought they loved her before she destroyed their family.
The thought of those two evil, selfish fuckwits sitting around deciding that they could cause all this pain and just wait it out until everyone came around and then play happy families with the children they are pretending they give a shit about is appalling.
She is not more glamorous or more kind than you. Kind? Give me a fucking break.
From the sounds if it she was jealous of you and your life and this whole thing has been her way of fucking it up for you and taking it all for herself.
Well she won't get it, because now everyone knows what a horrible bitch she is and what a worthless piece of shit she's with, and you'll still be you. You'll still be better than her, you'll still have your lovely children and you'll still have your life, just without a man in it that it now turns out wasn't worthy of you.
I'm so sorry you're hurting so much. You really sound amazing and strong, and lovely. I hope you get your life back soon. It won't be the old life, but it will still be yours.