Well, he's been having an affair with alcohol all this time, anyway. At this point, does it really make a difference? He's not someone you can trust. He's let you and your son down, over and over.
Envision this. You are drowning, going down for the last time. You have the opportunity to cut loose of a great weight that is pulling you down. Would you cut it loose to save yourself? To live so you can parent your child and give him a shot at a happy childhood?