There are phases in my life, when I smoke a lot (but never nearly as much as you) and phases with nothing at all. So I regulary start and stop smoking. The trick for me is, not just not do anything anymore - you rather start doing something different. Because your mind is used to the reward of the ganja - if you miss that, there needs to be something else. Other pleasant experiences.

Physical activitys help a lot, or starting to travel. But just stopping ... I believe is very hard on your own. In general, when I smoke a lot, I tend to isolate myself more and more. And when I stop, I socialice again. So that works for me (mostly, transition phase can still be hard, though). If you lack people who could help you, think about professional help...