Though Sandi hit the nail on the head, how long are you willing to endure the infidelity and at what point are you giving her the best of both worlds?
I don't think he is 'enduring' the infidelity-- he has moved out and is not pursuing his WAW. I don't think that being friendly and polite (not "friends"-- and HP, I would recommend not asking so much about her job, etc.) is not giving her 'the best of both worlds'.
There does not seem to be a benefit to HP OR his son by continuing to respond angrily OR ignore her.
