wlf...reading your last update I could only think "wlf's wife is living the consequences of her action" I say that as my IC has constantly when talking about my W spoke of how she must live with the results of her choices. clearly your W is doing the same thing. i think you are doing the best you can with your S's feelings towards mom. be supportive, but letting her and him handle their relationship alone is best.
it struck me that unless W is completely devoid of feelings she is heavily feeling the consequences of her action. now who knows how the cost/benefit equation in her head is working, but it would seem she is paying a heavy cost.