Friends wedding

I used to have this best friend for years. Her and I were really close. She started dating this loser 5 years ago and we stopped talking. Fast forward we are friends but I don't approve of their relationship. He's a controlling freak. They're getting married in October and she's inviting me. I was hoping she wouldn't. How do I turn it down? Do I tell her the truth? Or should I go? I absolutely do not approve of her marriage. 😐