He is insignificant. This is not about you, your w and OM. This is not about you and OM. This is not about your W & OM. This is about YOU AND YOUR WIFE. He does not matter in the end. For now, he's an inconvenience. A pimple on your back. That's it. He will go away. You must focus on you.
Don't even discuss him, none-the-less question her. You immediately give him some sort of credibility as if he could possibly ever know her as intimately as you have for the last 12 years. Be aware, but don't be consumed. He is a bandaid to her pain - all he can do is cover up the wound. You are the only one who can make it heal.
Me - 43 and She -36. No kids. Married 7 yrs - Together 14 yrs