Girl, you were smart enough to be able to see that things were wrong with your H that no amount of DBing were going to fix. I still think that if you read that book The Sociopath Next Door, you would see a lot of him in it. Personality disorders and serious character defects are not very fixable.
You're right to just move yourself along into a new life with your son. Just because it's not the destination you were expecting, doesn't mean it will be worse. More likely it will become WAY better and a MUCH better love is waiting for you down the line. Have peace in your heart that you made the right attempts to save your marriage, but this one is one that shouldn't be saved (and I almost NEVER say that to people!).