If she uses sex as a bargaining chip divorce the bitch.
Get the tux. It’s not a big deal. Nothing to fight over (and men do look hot in tuxes).
I remember my wedding, big deal, beautiful dress, ceremony, reception. Most importantly, the vows were taking.
I was a bridesmaid in a few weddings prior to my own and it was hell. I had one tell me how to wear my hair (up and I never wear my hair up unless I’m cleaning on swimming) and told her to shove it.
Two months after we were married, we were invited and my husband was best man at a black tie wedding. I never heard of a black tie wedding before, but he didn’t have to worry about it because he was the best man, already had to wear the tux. I wore the little black dress that always works for formal, semi-formal events.
Just wear the tux. She’ll appreciate it.