dude, i now a few people exactly like that, shoot i myself was an avid smoker for a good amount of time but i stopped. I only lit some up not to long ago just cuz it was a good friend of mind bday and he asked me too. But listen, people like that get to the point were it is technically an addiction to them, although its not even an physically addicting substance. Your mind gets to the point after smoking so much for so long that it needs it in order to fuction in day to day life. Its really sad. People say they will stop or say that they are ok, but they know they wont and they know their not. I had some friends that i recently just cut ties with who said they were going to stop smoking both weed and cigs. his reasoning was that he was going to work out. But, honestly not once did i believe them.

Although your a concerned friend and want to do what ever you can to help him, or tell him whats up. Ultimately its up to them, if they really want to quit or not. if they do and really have the drive to do it then they will. but if nothing else is going on in there life to where it doesnt matter if they do or dont, then they never will.