Dear 16 year old gentleman, during adolescence it is quite common that choices keeps varying,  what was good yesterday may not be good today, keep looking for better options so on and so forth. You as an individual do have other challenges to handle, strengthen your foundation by academic achievements, setting goals for your own life by setting high standards etc., and not getting stuck with thoughts of why your friend behaved so. She will move on while you will get stranded with this thoughts. Choice is yours, whether to focus on your growth or mess with your life.