You want advice on how to get a (very mature) 22yr old au par who you had a 9 month affair with.... back into your house and have your wife of 20yrs be ok with it. That's called a miracle. The laws of the universe don't work that way.
You could try hypnosis ....no... not for your wife for you. This NRE condition can be a very destructive force, and most people while under the influence can't seem to accurately calculate the downside of things until they've lost those things. So I'd be very careful. You need to look up NRE.
Good luck ... and please let us know what happens.