I really feel for you. My H and I were in similar circumstances with our son 7 years ago. Sad to say, it lasted a long time. And it nearly killed our marriage. My son is 25 now. Half the kids he was friends with in high school have died of drugs or accidents in the past 7 years.
Your husband is right. Even if you don't know what your son did last night, it probably could have killed him. I will tell you how our story resolved. My son was arrested for possession of marijuana twice when he was 19. The first time they didn't do much, and it didn't change his behavior one bit. The second time the justice system was serious. They threw him in jail, and we didn't bail him out. (First smart choice we ever made.) Then they put him in a 3 year diversion program with drug and alcohol testing, rehab classes, AA, and required him to finish his GED and get a job. (Hooray for the judge!) Anytime he fell down on the conditions of probation, he spent a few nights in jail. 3 years is a long time. During that time he started to grow up. His maturity was delayed by the drug and alcohol abuse.
His friends didn't get busted, they continued using. S25 went to funeral after funeral. He started saying that he was the lucky one. He understood that if he had not been busted, he would have died too. That's when we started to see him change. It took about 5 years to come out of the hole that he had dug for himself. But I am very proud of him now. I hope that your son will find new friends. Because without changing friends, the behavior will not change.