Man, I've been there. One of our bitterest moments early on (before we got married! How stupid can you be?) was a dance where she wanted to grind and dance like that all night, and I just couldn't deal with it, knowing that we were going to go home and I was going to get rejected. Again.
The problem is your options:
1. Don't go to the wedding. This is an option, but explaining why is going to be hell, and the truth is that it will amount to telling her she was going to reject you before she actually says no to sex--and before she even thinks about sex that night. This will not go well.
2. Go to the wedding. Play along, smile, do all the sexy dancing with her, and think of sex as a nice bonus that may or may not happen that night--something you can take or leave. Deal with the rejection if and when it happens. If this sounds farfetched to you, it's because it is. During an SSM, the HD partner wouldn't be nearly so miserable if he could just do this. The reason SSMs are still so common and so painful is precisely because it's next to impossible.
3. Go to the wedding but tell your wife honestly that you aren't going to do anything that betrays your integrity. So if she wants to act like you have a happy, playful, sexy marriage, that's her choice, but you won't play along. This doesn't mean you have to be a jerk or make an issue of your marriage problems in public, just don't participate in anything that strikes you as dishonest. Might lead to staying home. Might do no good at all. But it might be one more straw laid on the camel's back. It takes a lot of straws before the camel's back breaks and a LD spouse understands how much you hurt.
People may say this is childish and wrong. Maybe it is. Certainly it could be if you let yourself be that one relative nobody wants to be alone with at the wedding because they'll have to listen to his litany against his wife. But if you have the self-control to limit yourself to telling the truth and not helping her cover up truths she doesn't like, that's no different in my mind than what people say here about exposing affairs: "I have decided that I'm no longer willing to lie to cover for you."
