What is a good song about your ex dating your best friend?

A great song that captures the feelings of an ex dating your best friend is "Better Than Revenge" by Taylor Swift. The track expresses anger and betrayal over a close relationship being compromised. Another option is "We Are Never Ever Getting Back Together," also by Swift, which conveys the frustration of moving on while dealing with new dynamics. Both songs encapsulate the emotional turmoil of such situations.