He needs to stop drinking totally.. coke and alcohol together form another drug in the body.. i forgot whats its called.. but drinking makes you want to get coke. Its a trigger for getting coke.
He may start arguments before getting coke.. this is called emotional relapse.. its his brain wanting coke.. and is playing mental games with him.. and you create situations that are not there as an excuse to go and pick up..
If hes being nasty with his mouth and that. Just give him some ground rules or your leaving. Tell him no more alcohol at least for a few month. Theres a great app called pocket rehab. Tell him down load that.
Does he want to quit.