Aita For Exposing My Best Friend's Secret

AITA for exposing my best friend's secret relationship to her boyfriend and causing chaos? I never thought it would blow up this badly. It all started when I met Lisa about a year ago. We instantly clicked and became best friends. She was kind, funny, and always had my back. We spent countless nights talking about everything, even our crushes and secrets. One day, Lisa confided in me that she was secretly dating a guy named Mark. She said she was terrified to tell anyone because she thought her friends would judge her. I promised to keep her secret and supported her decision. Mark was a good guy, and I could see how much Lisa cared for him. But then I met Mark at a party one night. We hit it off and started talking. I could see he was genuinely into Lisa and that they had something special. I decided to keep my distance and not mention what I knew. I wanted to protect Lisa from any drama. A few weeks later, I noticed Lisa acting strangely. She was nervous, avoiding my gaze, and seemed tense whenever Mark was around. I started to suspect she was hiding something. Then I overheard her arguing on the phone with her sister about how she was planning to tell Mark the truth about their relationship. I was torn. On one hand, I wanted to support Lisa. On the other, I felt guilty keeping her secret. Then I got a crazy idea. What if I told Mark about Lisa's secret relationship? Maybe he deserved to know the truth from the start. So I did it. I waited until Mark was alone and told him everything. I explained how Lisa had confessed to me and begged me to keep her secret. Mark was furious. He said he had trusted Lisa completely and felt betrayed. He confronted Lisa immediately. The fallout was explosive. Lisa was devastated that I betrayed her trust. She yelled at me for ruining everything. Mark and Lisa broke up the next day. I thought I was doing the right thing by being honest, but I never expected it to cause so much damage. Now Lisa refuses to talk to me. Mark has blocked me everywhere. My friends say I am the villain for exposing her secret. I feel horrible but also feel like I was trying to do the right thing. Would I be the asshole if I had kept quiet or was I justified in telling Mark?