Like Mafioso said, most people quit smoking weed for a reason. Either kids, or wanting to get a good job etc. When I quit, I tried to keep my stoner friends. They offered me joints every time I came over, after about a month we lost contact. I got a good paying job, also got put on suboxone. I could not afford to fail a piss test at either of these locations. All my "friends" pretty much abandoned me when they realized I wouldn't be contributing to smoke anymore. I feel like a lot of them aren't really friends in the traditional sense anyway. They all hang out, smoke, talk for about an hour or two, then leave. If there's no smoke around, they dont hang out.
If your only connection to your "friends" is your interest in doing drugs together, they arent friends. You need to have more common interests than drugs.