I would never want to have my words "go be with the OW if you want to" to come back to haunt me. That addiction to the OW is strong, you do NOT want to encourage it verbally in any way shape or form. You do not want him to say to you someday, "Well, you told me to go to her if I wanted to. I figured you must not mind it that much."
Do more of what the books says in that if he is going with the OW, you leave the house as well...look good, smell good, GAL.
