Quitting smoking will only be difficult because a large majority of my friends smoke often and it's just become a part of my life and recreation plans.
Dogg it is really, really easy to just be like "no thanks" when you're chilling with people and they're smoking and they offer you the joint or bowl or whatever. You might get a few people halfheartedly complaining about how you're a buzzkill, but unless they are your best friend and they are only saying that because they're really, really used to smoking with you and genuinely miss the good ol' gettin' stoned and hangin' out ritual (and, as your established best friend, are within their rights to voice some degree of disappointment), this is actually just an indicator that there is no reason to ever
make them your best friend. Anyone who talks shit on you for opting not to smoke with them is a douchebag. With this in mind, you should find it no problem at all. ("I'm taking a break" is all anyone should ever need to hear.)
Alternately, you may discover that it is not smoking weed that makes you feel shitty, but rather, the nature of the situations in which you smoke weed (and therefore always coincide with your high). If you find yourself getting all anxious and depressed when you're hanging with your buddies and everyone but you is smoking, it was probably not the pot that made you anxious and depressed in the first place.
Halfway through college I realized that, ever since I'd smoked for the first time during the summer after graduating from high school, I hadn't gone longer than 3 weeks without getting high. I decided that if I still cared about learning about my mind (which was the goal I had when I started using drugs), I should probably take some time to find out what happens when I stay sober. I abstained from all mind alterants altogether for 3 months. It was a piece of cake, and it ended up helping quite a bit. I recommend that you go with 40 days ... see how you feel after 40 days of not smoking (and honestly I'd recommend not drinking either), and if you think you've figured some shit out, try it again and see if anything's different.
If this sounds like an unpleasant exercise in asceticism, that is actually a good indicator that you'll benefit from it. If, instead, it sounds like it really wouldn't be a big deal at all, that's also a good reason to try it out (proving yourself right will be worth it).