First of all, I am sorry your son is having to go through this. It sounds like you are doing what is best for him in terms of being there for him and moving out so he didn't have to be in that toxic environment.
I can definitely understand your anger in this situation. He is making himself the benevolent one in his head and trying to make you blame yourself by saying he was still open to a reconciliation etc. I bet he is feeling very guilty because he is not there for his son and his actions have caused a lot of the stress S is going through so (as many men do) they create fantasyland in their head where you are the bad guy and they have done nothing wrong.
Your S is lucky to have you and I am glad you realise that what your H is saying is BS. Somewhere in his brain he must know that what he is saying is not accurate and hopefully that piece of reality will tunnel its way out at some point.
You are doing great - hang in there!
Me 32/H 32 M 3yrs/T 8 yrs 0 kids and 1 dog Bomb 5/15/08 - wants to end it to pursue OW Seeing OW and moving out 7/08