just another hug from an internet stranger and a little advice (though feel free to skip it if it isn't wanted)....
While I am sure you know that it is so much better for this to occur now than after the wedding, I am also sure that knowing that doesn't really help too much right now. Allow yourself to hurt and to mourn the lost relationship. When I got a divorce (which did not involve such terrible circumstances...), my mom told be what her mom told when she and my father split (ummm, the circumstances there were closer to yours...): You may know that the man isn't right, maybe even to the extent that you don't mourn the loss of him, but you can still mourn the loss of the dream, the loss of the life you saw in your head.
Surround yourself with love. Or, if it is more your style, take some time alone. Be good to you. Feel it and note the feelings. Wallow. And then, in time, move on. I decided to give myself two weeks of full on wallowing and then I took a breath and worked on moving forward. That doesn't mean it never hurt afterwards, just that I tried to refocus.
More hugs. You'll get through this.