"I never post about my personal life but..."
These always start off that way.
And now since you have...
I would talk to her about putting off the wedding for awhile. Who cares if you have to change plans, inform family, etc. What matters is this decision, one of the biggest decisions you will ever make in your life. You should question her more deeply, though. Maybe she can't actually admit to wanting to end it all together? Bring up putting off the wedding, but ask her if it's even worth prolonging the situation. No, it won't be easy. Yes, it will suck fuckin royally, but it will be worth it in the end. Too many people get married for the wrong reasons or have second thoughts and don't voice or act on them. Look how many marriages end in divorce? Marriage is not always easy and you don't need to bring problems and doubt into one.
This is very hard to comment on online. Especially, since I don't like to type and try to shorten everything. I'm not doing shit, so if you wanna come by and shoot the shit, play some games, talk about it with someone who's experienced or whatever, let me know. I'll shoot you a pm. Just know that a hug may not be included.