Welcome. Its great that you are seeking support and information before you get married. That is a step that can complicate your life immensely.
Are you going to AlAnon or therapy? Either can be very helpful as you learn and try to make decisions.
Personally, I wish I had listened to those quiet little voices telling me not to marry an alcoholic. It would have saved me a great deal of trouble and pain. Now I am divorced, after not quite 5 yrs of marriage.
If I could go back in time, I would not have gotten married to an active alcoholic or one in early recovery. I would have insisted on delaying the marriage until he had at least a year of sobriety under his belt, until he had shown he was strongly into recovery and all that entails. I would not have gotten married if he was drinking at all.
Yes, alcoholics can get into recovery and stay on that road. My brother has been in recovery for 20+ years. But he works at it every day, even now.
Ask yourself if your fiance is the man your want to share your life with as he is right now, not as what you think and hope he can become, as he is right now.
Better to delay your wedding until you have no doubts than to marry and have a big legal mess to get out of it later.