I would love to read about a fight between your Fiancée and your "Friend". That being said, just bringing this up to your Fiancée could change your life. Wither that is in a positive or negative direction, I have no clue, but you may want to think through what may happen. Just telling her about "your friend" especially if sre does not know how flirty you relationship is with "your friend", could have enough of a change that it could effect your life.
Good luck, I hope it all works out the way you want it too.