First let me thank you for asking for me by name it makes me feel as though you trust me with your questions. With that being said I think you need to be honest about how you feel his drinking and driving and his substance abuse. Would you rather him know that you do not agree and you allow him to go on harming himself and possibly others. Tell him that you are proud of the steps that he has taken but you feel he needs help for his alcoholism and substance abuse or you are afraid that it will harm him and you will lose him forever. When someone is abusing drugs they usually go on to bigger and stronger drugs because their system has become so use to the drug of choice that he will need something stronger and you do not want that to happen so you should try to get a control of this now.
Tell him you are only doing this because you love and care for him and want him to get better so that you can make a life together and so that you don't have to worry about whether he comes home safe at night. It's very important that you try to talk him into getting some counseling for his abusing alcohol and drugs and may not be able to do it on his own and has a better chance of kicking these habits if he has you and counseling but if he has a DUI the courts may order him into counseling as part of his sentencing. Make sure you tell him that you will be there for him and make sure that you are totally involved in his recovery if that is what he chooses to do. Keeping a closed mouth is not the good thing to do because he may take that as you accepting what he is doing and that isn't the impression I get from what you have told me.