This is really difficult. Just as you can't change your son, you can't change your husband.
I'd suggest attending a few AlAnon meetings together, then explaining to your husband why you feel you can't live like this anymore. If your husband is not willing to change his behavior, you'll need to make some tough decisions for yourself.
Each partner will take a different path to determining their own limits. My husband and I went back and forth for years with one of us enabling and the other being tough. It caused an incredible amount of stress on our marriage. What finally worked for us was to get a professional interventionist involved, He talked to us together and individually, and then held a family session with us the day before the intervention, making sure everyone was on board and united. It wasn't cheap, but it gave us a formal framework and process to follow, so that when we told our son that he could not do drugs and live in our house it was done with love (not anger) and there was no waffling.
Your husband may not be at the point yet where he can do that - and professional help may not be enough to get him there. If he's not on board, but does it anyway - and then your son gets killed on the street - that will create damage to your marriage that may never heal.
If you are thinking about kicking your son out so he hits bottom and gets better - that may not happen. Making a decision based on forcing an outcome is not a good idea. If your husband wants to keep him home to keep him safe- that may also not happen. Addicts die in their beds, and they die on the streets.
Whatever decision you and your husband make needs to be based on what's best for you. Do what will give you peace. Hopefully you can get there together.