It sounds like the OM knew that your wife was going to be alone tonight and you were going to have the kids. He was probably trying to coordinate plans etc!! I personally would have called her on that possibility when the phone was going off. It would have put her on the spot with the kids. I know that some will say don't involve the kids...and I agree but that doesn't mean you have to protect you WW as well when its in their face. Anything to further blacken her relationship with OM is always a good thing. Who knows she may not be hooking up with him tonight but his persistant calling has to be nipped in the butt....call a spade a spade.
Look you have done a good job creating a positive enviroment with your wife along with showing her what she may be giving up with the family interactions you all have shared lately. But if her latest comments are to be taken seriously...then maybe a pullback is in order....a ying and yang effect to give her a taste of the negative side of the end of the family unit and its effect on the kids....deepen her guilty conscience.
Wayward wives tend to need to remain friends with thier betrayed husbands when children are involved....just to show their kids that she is not the one ending the family but you have both agreed to this and that you both will continue to have family time. Specifically that she is not the one doing this but both of you are etc.
The war is not over, just keep probing her defensive line and exposing her weaknesses...and most importantly the weaknesses of her allies (The OM). Maybe I did learn something in the military!!