YOu ARE reasoning with an addict my dear... Infidelity IS an addiction like all the others... dangerous, destructive, and selfish....

The list is a good start.
He's going to respect consequences a lot more than your feelings right now
If he has to get a drug test done because he chose to introduce your son to OW then he may think twice
He's not forgotten you told him, he's just being passive aggressive... most of them are about this stuff
The thing is, he has consequences he can hurt you with - you son
You need something to bring him back in line and cooperate with you... Right now he clearly isn't capable of negotiation without leverage of some sort on your part