Hi joanne. 1st of dont be a guarantor. Do you really need the stress if he does not pay. And secondly he really does need to want to quit. Otherwise its pointless. alcohol is a main trigger for coke , so if hes going pub after work he will be getting coke maybe.
Id have a word with him and lay some ground rules. And make him aware of the drug. Id could give you advice on how to stop but there is no point just yet, if he does not want to. Feel free to ask me anything.