I understand your point but TBH I can't say for sure how I would react. I'm sure I would be very shocked but if it was her seeing a "professional" for the one off without any of the emotion attachment; I would be a lot better with that as I wouldn't perceive it as a threat to maintaining our family unit or as emotionally cheating. However, I would definitely be upset by an affair involving a continuing relationship....What if she is having casual sex on the side, and you happen to find out. I know that to us it would be absolutely unacceptable...
Sorry to the OP for derailing your thread!