Grabbed the microphone at my engagement party

AITA for exposing my fiance during our own engagement party because his ex showed up uninvited. I need to explain everything from the beginning. Marcus and I had been together for three years. We were finally getting engaged and threw a huge party with family and friends. Everything was perfect until his ex girlfriend Jenna walked through the door. Nobody invited her. I asked Marcus who told her about the party. He said he had no idea and looked genuinely confused. I believed him because he seemed just as shocked as me. Jenna walked straight up to us smiling like she owned the room. She hugged Marcus a little too long for my comfort. I brushed it off because I did not want drama at my own party. Then Jenna raised her glass and said she wanted to make a toast. Marcus tried to stop her but she was already talking. She said she was so happy for us and that she always knew Marcus would find someone eventually since she broke up with him two years ago. Everyone laughed awkwardly. I forced a smile too. But something felt wrong in my stomach. After the toast I pulled Marcus aside and asked him directly if he invited her. He swore he did not. I wanted to trust him. We went back to celebrating and I tried to enjoy the night. Later I went to the bathroom and overheard two women talking outside the door. One of them mentioned that Jenna had been texting Marcus for weeks and that she showed them screenshots. My whole body went cold. I stayed frozen behind that door listening to every word. They said Jenna told them she was sure Marcus still had feelings for her and that the engagement was a mistake. I walked out of that bathroom shaking. I found Marcus by the drinks table laughing with his groomsmen like nothing was wrong. I asked to speak with him privately. He said we could talk later after the party. That answer made everything worse. I grabbed his phone from the table while he was distracted talking to his brother. He never uses a password because he trusts me completely. I opened his messages and found the conversation with Jenna. There were weeks of messages. She said she missed him. He replied that he missed her too but that timing was bad because of the wedding planning. My hands were trembling holding that phone in the middle of my own engagement party. I did not know what to do. Should I confront him quietly or let everyone know the truth. I decided everyone deserved to know what kind of person he really was. I walked to the center of the room where the microphone was set up for toasts. I grabbed it before anyone could stop me. I looked at all our friends and family staring at me. I read the messages out loud in front of everyone. Marcus turned pale white as I spoke every single word from that phone. Jenna tried to leave the room quickly but people blocked the exit wanting to hear more. His mother started crying. My mother looked like she wanted to disappear into the floor. Marcus tried grabbing the microphone from my hands but I stepped back and kept reading. I told everyone that our engagement was built on a lie. I told them Marcus had been talking to his ex for weeks planning to keep both of us close just in case. The whole room went completely silent except for Jenna quietly crying near the door. Marcus finally admitted everything was true in front of everyone. He said he got scared before the wedding and reached out to Jenna for comfort. He said it meant nothing but words on a screen say otherwise. I took off my engagement ring in front of every single guest and placed it on the table. I walked out of my own party alone while everyone stared in shock. My family followed me outside leaving Marcus standing there with his mouth open. Now people online are split about what I did. Some say I should have handled it privately instead of humiliating him in front of everyone. Others say he deserved every second of that public exposure for betraying me during our engagement celebration. Was I wrong for choosing to expose him that way instead of confronting him quietly first.