First of all, you can be an athiest and work the steps, lots of people do.All you need is to have a "higher power" to hand things over to.For alot of people it is Nature/the universe/circle of life..I mean nature is truly more powerful than any of us.It really is just an aid in letting go...there are lots of old threads here that you can look up on that subject if you'd like.
Some of the things you said are so right on..like YOU are NOT helping his drinking..that is manipulation to get you to stay plain and simple.Alanon can really help you see more clearly what is enabling and how to take care of yourself..also agree with the Codependant No More suggestion.
As for when to leave, only you can decide that, but maybe when you want more for yourself, want a serene home for your little one, when the pain of staying is greater than the pain of leaving....