What can I do to stop smoking weed?

I've been a habitual weed smoker for the past few years, but I'm looking to quit, or at least take a break from it. What can I do to motivate myself to stop smoking? It's NOT an addiction, because I know I have enough willpower over my vices. My boyfriend and most of my friends smoke, so it's not an option to cut them out of my life. It's just hard that when they pass me the blunt, it's hard to say no! (and No dumbass comments please, like smoking is lame and for low-lives, I've heard that enough!) What can I do to find the motivation so stop? I'd appreciate any advice. thanks