Boyfriend (M28) has admitted he has a drug alcohol and smoking problem. How do I (F21) help?

Hi guys me (22F) and my boyfriend (28M) have been together officially around 2 months. We met during my internship and he was a subcontractor working on the same project. I have met his family and they seem to like me. He has mentioned money problem which I did not understand at first since he is a high paying senior engineer. I am a student studying engineering. He has asked me to go 50-50 with him which I refused, and now admitted he wants to stay but wants me to help him with his drug problem. I don’t know how to help but I also don’t want to leave. I stay over at his house 3 nights a week and he takes me to class since he is working next to my university. I am not not sure how to navigate this situation.

TDLR: Boyfriend has a drug alcohol and smoking problem and wants me to help. How do I help?