Punishment for the Traitor

I went to listen to my junior's live performance. At the after-party for the live show, my junior Ryohei became close with a girl named Kanako and they exchanged contact information. Ryohei seemed to have fallen in love with Kanako at first sight, and all the band members decided to support him. Ryohei and Kanako began talking on the phone from time to time. However, one day Kanako's behavior became strange and she grew distant. When Ryohei asked her what happened, Kanako refused to answer. Then one day, I came to learn the reason why Kanako had become so withdrawn. There was a truth that could be called a betrayal. What action did I take upon learning this truth of betrayal!?