Why would two women want to use me as a scapegoat?

I just learned that someone who I thought was my support system is not. She has been backstabbing another lady so that I would not like that lady. She is very two-faced. It seems she wants me to continue to hold a grudge and not be a friend to someone so that she can be her friend. She and another had issues and wanted me to get in the middle because I had issues with her too. My issues would have been just what they needed for me to work on their behalf.