There is always your side, his side, and somewhere in the middle lies the truth. Your son has a different experience than you had, its valid. By your own admission you were the raging lunatic in the house. Your son is too damn young and inexperienced to understand what happened here, some of what was going on is not the business of a child no matter how old- for now anyways. Shame on your husband for using him. I am unsure why he is blaming you for abandoning "them" when it is your husband that chose to leave unless Dad has once again manipulated the truth.
The tie between a parent and child is so strong, and very hard to break. Take marie's advice and let the dust settle. Just leave him alone. Now you start your own recovery, the best you can do is to "best" yourself. Your son is not gone forever by any means. In fact now that Dad is leaving.........your son is going to be exposed to things he wasn't before because much was hidden by you. More is always revealed.
Stay strong Amy, life is very hard sometimes. I'm going through it myself (not alcohol related or relationship related). 1) you will deal with this 2) a new chapter in life is always a good thing 3) you can and will recover and be better 4) Someday....you will look back and be thankful that you were set free.