I'm so sorry that your family is suffering. Would your husband consider getting treatment? If not, one suggestion I have is for you to talk to a chemical dependency counselor about doing an "intervention" with him, where you and your son (yes, your son, too, even though he's young) and anyone else who cares about him, tell him how much you care about him, but how his addictions are affecting you. I've gone through this with my mother and we did, at least, get her into treatment. For yourself, find an Al-Anon group which is for those who are living with or affected by people with addictions. It will help you cope and also teach you how not to enable this behavior. He can get therapy for the grief and depression, but if he's still drinking and taking drugs, it's not going to help.
You need to take care of yourself and your son - that is paramount. This is especially harmful for your son, especially if nobody is talking about what's going on. You could also consider therapy for him or both of you to help deal with this. If you need help finding resources, let us know. You can even call a crisis line to start with and they can probably get you connected with the right resources.
I wish you all the best and hope that your husband will get help soon, for everyone's sake, especially your son's. I hope you'll let us know how you're doing and what's going on.