I think you should really evaluate getting married to him right now. LOVE will not change the addict.. only professional help will. If he's not in that place, then why should you sacrifice yourself at this point in your life? I agree with other posters. See what he does with his addiction. It only takes weeks for you to see the direction he will take. Either he will choose recovery (which will take months, even years to get right) which will call off the wedding anyway and/or he will continue to use (which is definitely no cause for a wedding).
Much hugs to you at this time. I know it's rough but it sounds like no wedding either way you look at the situation.