She's trying to assure you that they are not trying to replace you with OM because that is exactly what they are trying to do.
You need to be very firm with your wife as much as OM. Dont discuss the issue or argue with him, he needs to see scary consequences and high costs for trying to steal your family or he will just continue to get bolder. And dont fall or react to your wife's hysterics. Your wife will likely resist, become enraged, accuse you of being controlling or paranoid, blame-shift and guilt-trip you. You don't argue your position or your feelings to her regarding her inserting him into her and your life, just enforce your boundary. I promise if you stand strong and dont let her affect you, you can outlast her.
You cannot keep her away from OM, but you can keep him away from your home and away from your children. That is a boundary well within in your right to enforce. You are the alpha gorilla here, its your job to drive this guy off from what is yours.
