Does your fiance sound like an alcoholic? To me, yes and unfortunately this is a progressive disease and without a strong recovery program, he will continue to drink more and more. And, he needs to seek recovery for himself, not you, not anyone else.
Also, keep in mind that you really have no idea what he is drinking when you are not together, alcoholics lie, they always minimize how much they are drinking.
Nothing wrong with postphoning the wedding again, it may be the smartest thing you have ever done for yourself, please proceed with caution.