I've always found tobacco use to be a very environmental thing. If I'm hanging out with a lot of smokers, I am much more likely to smoke habitually. I live with someone who smokes neither marijuana or tobacco, so if I've been staying in a lot not doing much (or hanging out with a nonsmoking crowd) I don't get the urge to smoke, unless there's some cue, like a person (actors mainly) I admire smoking, which I admit is pretty lame of me, smoking to be "cool" but not gonna lie, some really really cool people smoke. Or pretend to smoke for drama at least. This is opposed to marijuana, which I am perfectly happy consuming on my own, in fact I sometimes prefer it.
EDIT: Oh sheesh it's a spambot isn't it.

He didn't have all the garbage in his signature when I first replied.
I personally recommend checking oneself for OCD at least once every 5 minutes.