Zanna, I think it's completely understandable (though regrettable) to have had this knee-jerk reaction to such unsettling news. I'm truly sorry for your loss and also sorry that you drank over it. Good on you for coming here to fess up. You know it's totally natural that your first instinct would be to omit that information - I think that would be the case for any one of us. It sure would be, has been for me.
In the case of your fiance, I'd suggest having another think about that one. Does he need to know? Right now, probably no. But what about a year or three years down the road when you inadvertently let something slip about this lapse? Or you don't, but you start feeling guilty that you never told him? As he is your soulmate, he surely has your back through thick and thin. And though he is not an alcoholic (thank the Lord, right?), surely he has enough compassion for you to imagine how you might have felt you needed to drink?
I don't know... I just think it's never a good idea to keep secrets from spouses, unless they are good secrets.
And hey, no offense taken here, I can barely associate the word "president" with the man. Enjoy your cocoa and tunes.