Once she has a taste of the OM and wants more, then I will tell her she can continue it outside of my house. I will do so unemotionally and state it very simply. I have earned this simple thing at this point.
She is not looking for another mate - this is all about sex. The OM is married, lives across the country, and has no immediate tie to our family.
She is looking to experience freedom for the first time in a long time.
She is looking to have sex with another man, you are looking at this logically and trying to rationalize her actions and I told you to stop thinking the way you think, she doesn't think like that at all. She's different from you. She's a woman, you're a man, you need to embrace that different thought process.
Once you step down as the man in her life and she experiences sex with another man, that one weekend with that one man may be over but she won't stop there. She will miss it and she will pursue those feelings that she experienced with him with another man locally in your area. Why? Because you allowed it and she knows that you value your marriage more than she does so that she knows she can disrespect you again and you'll always be there, good ol' reliable Mike, the safe backup plan for the times when she needs a break from sex with other men. You don't know what attraction is about, you don't know what causes it and what kills it.... actually you know already what kills it, and you continue doing that.