If you think you can still be friends with addicts/users, you are mistaken. If they can't get clean, screw them, they will only pull you down.
I suppose it can work with hard drugs or alcohol - I am not, and never was, a user or either, so I'm no specialist though.
However, I AM a nicotine addict. I say nicotine and not tobacco, because I have switched to vaping as a risk mitigation strategy (and quit smoking for good as a result).
One thing I can tell you as a former smoker is, when you're hooked on tobacco, there's no escaping it. You can't avoid being with other smokers, because the smell of cigarette is everywhere. When I quit smoking, it'd only take some random guy who had just smoked outside, walking past me, reeking of cold cigarette smoke, to send me craving like there was no tomorrow.
Random guys who smell of tobacco are everywhere. You just can't escape the smell. You're constantly bombarded with reminders that, yes, you'd really REALLY want to smoke one just right now.