I'm really glad you've been able to reach out for support with this, it sounds like a tricky situation to be in. I actually had a similar experience with a past partner, so I can totally understand the difficulties that can arise whilst going through this.
I think your concern and want to help him really shows how much you care about your partner, it's great to see you are supporting him through a tough time. However, its also super important to look after yourself, and feel like the support you give out is also given back to you ❤️ It can be really difficult to stop from going over that line of being supportive, to taking responsibility for. The choices he makes are his and at the end of the day, the only person that can make the changes in his life is him. I imagine him thinking you were being manipulative because you wouldn't drive him somewhere was really hurtful. How is the relationship feeling for you?
You've mentioned he would be happy to reduce his smoking, is that something you feel like he really wants to do? Have you been able to have a chat with him about what support he would need to start making that change? We have this article that gives some tips on how to support someone with a drug additction that might be helpful. SMART Recovery has support meetings for both the person and their family. Counselling Online provide free 24/7 counselling for people affected by drug use too. 🙂