Maybe you should confide in your fiancé at least you will have someone to confide in. No sense hiding it from her , for the simple reason if you don't stop and get deeper into drinking - she will find out anyway . If you really truly want to stop , you need to make a plan and stick with it .
There's treads here where you can get ideas , and read others that are going through some of the same things .
One day at a time is how most do it . Good luck don't give up find ways