>But quitting is really hard. I'd successfully exhaust my supply, but there's always bowl- and grinder-scrapings. After a night or two of smoking tar and dust, "fuck it", I'd find some more.

I've found my attempts to quit go better when I actually have a large supply of it that I'm consciously choosing not to indulge in. When your supply is exhausted your brain goes into a bit of a panic mode about it and you can't think rationally about how/why you're quitting.