Geez Jar, I'm really sorry that today has turned out to be a crapper.
It's incredible that she thinks you would want to be best friends with someone who betrays you, lies to you and uses you. Apparently, she is sooo wonderful that all that other stuff shouldn't matter.
Perhaps your best revenge against OM would be for her to marry him. Seriously though, she is reacting to your change in behavior. She is afraid of the change and is trying to counteract it.
Keep being the responsible, consistent, positive force in your Ds' lives. They are going to need it.