Wow. What a rotten turn of events. I am so sorry this has happened to you. I can certainly see how you would be shocked and appalled by all this.
There's just not a solution here that's clean, quick and painless, at least not that I can see. That being said, here's what I would do:
- proceed with the wedding as planned
- tell my parents (and any other concerned parties) that nothing has changed except what they know about my/our love life, remind them that, as an adult, I think and choose and act for myself (as does my fiance) and that as much as I want them present to celebrate my wedding, I would understand if they choose to not participate or be present
- prepare to do the same with anyone else concerned (or else get out in front of the avalanche by outting my tribe at a time and place of our choosing)
- keep my ears and eyes open for the identity of the person who has chosen to stir the stink at our expense. When s/he reveals him/herself, I would express my genuine opinion of his/her actions in this matter (in clear and specific terms, if you know what I mean), then promptly expel the troublemaker from my life.
Best of luck to you, whatever you decide to do.