Hold on a second. I don't see how saying "you did choose him" is BLAMING anyone for anything. It is a fact. She did choose him.
Honestly, I think you are looking for a professional to validate your wanting to leave. You don't need some PhD to give you permission to leave. You don't need a second opinion. You don't need us or your AH to give you permission to leave. All you need is to honor yourself and do whatever is best for you.
Instead of wasting money on marriage counseling to try and fix a marriage you appear not to want to be in anymore, maybe you should save it to make a better life for you and your son.
My two cents,
L