Don't be alarmed by the threats, he is just doing what addicts do. They have the attention span of a 3 year old and seldom follow through on any threats that have to do with the legal system or taking care of their children.
When you finally leave him he will spend all his time and effort trying to figure out how to get money to buy drugs. In his current state of mind, he is only attempting to use the child as a weapon, he really could care less about either of you...he is too far along in his addiction, it's all about him and his drugs.
He is 41, with the emotional IQ of a 13 year old, he is a child in a mans body. Go about your business, he is not going to change.
Keep posting, it will help.