notice how much unrest this one "statement" has caused you. by an active alcoholic, swearing the oath..........again. as if it were God's truth.
remember also, he said this to you - not to DS. and you have no control over what he DOES say to his son. you can only provide your son with information regarding the disease, it's affects, and how those in active addiction might behave. you do not need to repeat the oath to him verbatim........or at all.
you also cannot predict what your AH will say or do with absolute certainty, nor can you predict how son might react. you have future tripped yourself way, way down the road. based on a few words out of his mouth.
ask yourself WHY are you reacting so much to his words? and why this time? your son is 15. he is the child of an active alcoholic. he may be a lot more savvy and aware than you give him credit for. it's not like any of this is NEW to him. it's what dad does. it's the kind of things dad says.