Imageer is right and has shed an interesting light on this.
As idicated by others, the OW is at least for now, of low moral character. Your H knows this and is pushing it out of his mind for now. He refuses to see her for what she currently is. He prefers instead to see her as a welcome distraction from his own internal issues. Working together made this very convenient for both of them. The sneaking around, the drama, it all adds to the fantasy. It all fades. The illusion will give way to reality. And does she plan to leave her family, or just share in your H's virtual escape from reality?
Is he affairing down? Yes. Does he know it. Not yet.
