Played his mistress's voice at our engagement party

AITA for exposing my fiance at our own engagement party in front of everyone. I need honest opinions because my family thinks I ruined the best night of my life. Let me explain everything from the beginning. My name does not matter here. What matters is that I spent two years planning a life with a man named Derek. He proposed on a beach in front of a sunset and I cried like a fool thinking I had found my person. We set a date for the wedding and started planning an engagement party to celebrate with family and friends. Everything felt perfect until three days before the party. I was looking for a charger in his gym bag and found a phone I had never seen before. My stomach dropped immediately. I opened it and there was no passcode. Inside were months of messages with a woman named Priya. They were not just friendly messages. They were plans for trips, declarations of love, and photos that made my chest feel hollow. I sat on the bathroom floor for almost an hour just staring at the screen. of me wanted to confront him right there, but another part of me wanted proof that could not be denied or twisted into some excuse. So I decided to wait. I copied every message and photo onto my own phone and said nothing. I smiled through dinner that night like my entire world was not falling apart. The night of the party arrived and our backyard was full of string lights and flowers and nearly eighty guests. Derek stood beside me looking proud, holding my hand like he owned me. His parents gave a toast about loyalty and commitment. My own mother cried happy tears. I felt like I was living inside someone else's dream. When it was my turn to speak, I took the microphone and thanked everyone for coming. Then I said I had a small surprise for Derek before we cut the cake. I connected my phone to the speaker system that was already set up for music. Instead of a song, I played an audio message Priya had sent him just two days earlier. Her voice filled the entire backyard, saying how much she missed him and could not wait until the wedding was over so they could finally be together without hiding. The silence after that was unbearable. Derek turned pale and tried to grab the phone from my hand. I stepped back and looked directly at him in front of everyone. I asked him calmly if he wanted to explain to our families why his phone was full of messages from another woman. His mother gasped. My father stood up so fast his chair fell backward. Derek stammered something about it being complicated and that it was not what it looked like. I asked him to look me in the eyes and tell me the truth. He finally admitted he had been seeing Priya for almost eight months. Eight months. That meant he was seeing her before he even proposed to me on that beach. The engagement party turned into complete chaos. Guests were whispering, some were filming on their phones, and his mother was sobbing into his father's shoulder. I calmly removed my engagement ring and placed it in his hand in front of everyone. I told him the wedding was officially canceled and walked back into the house, leaving him standing there holding a ring and a secret phone that was no longer a secret. My own mother says I handled it with dignity, but his family is furious that I humiliated him publicly instead of ending things privately. They say I could have broken up with him quietly without destroying his reputation in front of our entire community. My sister says he deserved every second of that embarrassment after lying for eight months. Now some of our mutual friends are taking sides and it has become a messy situation that feels impossible to escape. Was I wrong for choosing his own engagement party as the moment to expose the truth, or did he bring that humiliation entirely upon himself through his own actions.