What country are you in? I'm in Thailand - and there are a couple of al-anon meetings (all too far from me).
Anyway, my AXBF was a binge drinker and a daily drinker when we met. Everyone told me it was part of his Aussie culture. He said he had done IV speed ten years ago but that wasn't what he wanted in his life, etc. And I knew he had smoked a lot of pot with his exgf. Since with me, he was only drinking, and his big long nights of drunkeness were getting farther and fewer between. I thought it was getting better. Then my last trip back home, he started smoking kronic (synthetic pot that was legal and is now illegal in australia) and when that became unattainable, he started buying "hush" herbs, which as far as i can tell are harmless placebo. When I got back to Australia, he apologized for our fights on Skype and said they were from smoking all the numbing herbs because he missed me. Whatever. I said, okay, they are legal so I'm not going to make a big fuss, but cut it out, it's a waste of time and money and it just looks stupid in general. I thought that was the end of that. Then one day he gets sent to work with this guy he knew from 10 years ago. Just a 2-day job there. And the second day he comes and is slamming beers and chain smoking. I'm in the middle of cooking his favorite meal and then he doesn't eat. It's a Monday night so I go to bed and he's still not sleepy. I wake up at 4am and he's upstairs jerking off to porn on the laptop. I ask him what's going on. He says his friend "gave" him speed and he ate it and can't sleep. By 7am, I have found his injection materials and he admits to buying $xxx worth of speed. He left me and went to a hotel and injected all of it. It took him over a week to come down and he didn't go to work in all that time.
I can see now that the alcohol is a problem. The small step-stone leads back to the bigger ones. All the underlying problems of OCD and crazy anger/happy love, those moodswings. It's all related.
My AXBF isn't a monster. He's a wonderful, sweet man I love so much. He never hit me, he's always sorry, he always says he's going to do better, that he can't live without me, that I'm his special little Munchkin. He and I used to talk daily, and he was financially supportive of me, bought me presents, took me on holidays. I love him without a doubt. It's the monster in the addiction I don't love. I know he's in there somewhere but I couldn't find him when he was high. I couldn't see my special Schmooples. He was gone.
It must be horrible to see your wedding day approach and to have this on your mind. And you wonder if you're just crazy. It's just a little pot right. It's just a little beer. It's just once in a while. You want it to be okay because you love the person.
Advice here seems to revolve around leaving them and getting your own life. Easier said than done.