Has a friend ever betrayed you? If so what did you do about it?

I had a friend who betrayed me when I was a teenager. I thought it was great how her and my boyfriend were getting along. I was so naive. They had gotten together behind my back and she was even living with me and my parents. I remember I drew a picture of her getting knifed in my diary. I know it's not connected or anything but years later some guy killed her. Our friendship and her life was more important than some teenage romance. I wish i had been on good terms with her when I last saw her.