Purr, I'm very sorry that you had to receive a call from the wife of the man having the affair w/your wife. You think that your spouse is being honest w/you and then this. Purr, your wife, the one you love, is still buried deep within her. Keeping this affair secret isn't normal. This really isn't normal behavior by any stretch of the imagination. She's testing the waters and is keeping you on the sidelines just in case this relationship doesn't work out.
Purr, I wouldn't contact your wife right now. I'd take some time for myself and do what I needed to do to get over this shock. In fact, I would sit back and allow the wife of the om to confront her. I think she needs to face the consequences of her actions and this would be a rude awakening for her to be confronted by the wife. Another thought, but I don't know how it would go over, but it's been done before, is that you and the wife confront them together. It has worked before. But, for now, do for you. Your heart, soul and emotional state are very wounded. Once you are over the initial shock, then think about what you want to do.
Purr, we all understand how you feel. I'm very sorry that this was the last piece of the puzzle that now confirms a crisis of some nature. Please take care of yourself.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.