Premature doesn't begin to describe this Mike, and I think deep down that you know this.
My only hope is that no other newcomers view this thread (and it's companion in Newcomers) and somehow come to believe that consenting to a spouse's desire to travel across country to have sexual relations with an old friend is a reasonble approach to solving their marriage problems.
Perhaps your story will surprise us. Maybe your situation is that one in a million where agreed upon infidelity is actually the key to rebuilding a marriage. You will pardon us I hope if we don't place much money on that however.
Your best approach right now would be to pack the remainder of your wife's belongings and have them waiting by the door. Change the locks on the house and when she arrives home, open the door only long enough to allow her to gather her things.
Don't trivialize your mistake here by in anyway suggesting that this is for your son. You made this decision because it was the one that did NOT require you to stand up to your wife and what she was proposing to do.
I don't wish misfortunane on you Mike. I have experienced divorce and betrayal - I wouldn't wish it on anyone. I'm sorry that you allowed your contribution to the marital mess make you think that the answer was for your wife to join you by making serious mistakes of her own.
Blessings,
Bill
"Don't tell me the sky is the limit when there are footprints on the moon."