J.,
I do agree with "Johnnie" and the advice she gave you.
You did the right thing by leaving and you're also doing the right thing by trying to keep your son from this damage. Is there any place you can move to out of the state? Some family perhaps who can help out with your son's care?
My first husband was like this and I stayed married for 12 years with 2 kids. When the divorce was final he moved to England to take a job and we don't hear from him. It's been 8 years. He is very "all about himself". I never did anything right, neither did the boys, he was not big on gifts or aknowledgment of any kind unless it was infront of other people. (Just like you were saying). He would suddenly become father of the year or husband of the year, and when people were not around, he treated us like we had a disease that he didn't want. He would come home and either "let" me give him a hello kiss or he'd turn his cheek. One day I gave him a light slap instead of a kiss and told him that I was not his mother and I will not be kissing him ever! It is best that you got out of there - I will pray for you and your son - it is a nightmare to be with someone who has a personallity disorder and can't be helped.
God bless and best of luck,
D.