My sister looks a little weird lately

My sister has been acting a bit strange recently. She often sneaks out in the middle of the night and is always mysterious when she comes back. I wondered if she was out there with someone, so I decided to follow her. That night, I secretly followed my sister and found her going to a bar. After she walked into the bar, she struck up a conversation with a man. The two chatted very enthusiastically, and it didn't take long before they entered the box together. I hid outside the box and eavesdropped, and heard them doing indescribable things inside. My sister's voice sounded like she was enjoying herself, and it made my blood boil. I really didn’t expect that my sister, who usually looks serious, could be so coquettish in private. I wanted to rush in, pull that man off my sister, and give him a good smack. But I didn't, because I knew it would only make things worse. I could only endure my anger and continue to eavesdrop. After a while, I heard my sister's voice getting smaller and smaller, and finally, she started moaning. I couldn't bear it any longer, kicked open the box door, and rushed in. I saw the man lying on top of my sister. My sister's face was flushed and her eyes were closed tightly. Furious, I grabbed the man by the collar and pulled him away from my sister. I raised my fist and hit the man in the face. The man was beaten until his nose was bruised and his face was swollen. He fell to the ground and couldn't get up. My sister was so scared when she saw me coming in. She quickly got up from the bed and ran to hide behind me. I looked at her and said angrily: "You shameless person, how dare you do such a thing!" My sister lowered her head and did not dare to speak. I know she must regret it now. But I won't forgive her because she let me down so much. I turned and left without looking back. I know that my sister can only walk on her own in the future.
#sister