Is it my business to know about my bfs drug habits

Is it? Whenever I want to talk to my bf about what he’s taking, how much, where he’s buying or anything like that. He gets mad and says it’s none of my business. He used to be addicted to heroin and stuff and he’s sober now but he still smokes weed and takes depression medication. He didn’t tell me about him taking etziolam until I caught him. Apparently will tell his friends but not me. I don’t get it