Hey Liz-
Haven't you already made your thoughts and feelings about his drinking and behaviour known to him many times? I think, based on what you have posted that he knows very well how you feel and how you feel doesn't matter to him. He's heard it...all before.
You are very right when you say that staying married to him is ok. Whatever you decide to do is ok. I think staying married IS what you want. But from the outside looking in, I think staying married will necessitate you accepting him exactly as who and what he is. There can't be any realistic hope for change. He didn't just happen, this has been your married life experience with him. I wish you happiness however you find it Liz. You and your Son deserve it, but be realistic.
The other thing I have been wondering is why you seem to be concerned with treating him only with kindness and love and without accusations as though he is a child. Why not just lay it out? Let him know that you are standing up for yourself and Son and you need change. Let him know that you are serious (if you are) Please don't be a doormat. I say all this with kindness.