I am very close to my brother's girlfriend. She is two years older than me and like a sister. My brother loves her so much and often brings her to our house. One weekend,she said she couldn't visit us as she had to travel upcountry with her family. But that same afternoon,as I was leaving tutorial class, I saw her with another guy and they were holding hands! I was shock! I tried to hide but she saw me. She said the guy was just one of her gay friends and begged me not to tell my brother. I don't believe het but don't know what to do?