Wow, I am feeling for you. Too bad it all happened at such a crunch time, where to make changes will be a real inconvenience to say the least.
This brings up so many questions and issues! Big picture, like "What is the definition of marriage, and who defines it?" and "If a wedding is a celebration of Love, what is Love, and who defines it?" Then the smaller, more personal questions, like, "Who in my life/family really loves and supports me unconditionally?" and "Who can I trust?" and "Whose fucking business is it what I do in my bedroom, anyway???"
I wonder, are your fiance's parents are open-minded?
We were involuntarily outed recently, too. It hurts, it's confusing, it's devastating... yet there was some freedom in it, in a weird way. A little bit of relief, after the dust settled. I am a person who wants to love out loud, and it's hard to be in the closet about a person who means so damn much to me and my husband. It may be tough but I can take it -- I can walk in the Truth in ways I never thought I could. However -- we think the "bleeding" has stopped, and we are hoping our privacy has been salvaged from here on. We now have time to prepare ourselves for the possibility of it getting out to more people, eventually. That involves asking ourselves some of those questions, big and small, so that WE will be rock solid in our "defense," so to speak.
My heart goes out to you.