Your best friend could be demonstrating Avoidance. Avoidance is a form of defense mechanism characterized by a person escaping or looking for a way out of an uncomfortable situation. It was also described as coping without really coping. When a person avoids a stressful situation he or she neglects to determine what is the cause of his or her anxiety. In this scenario, your best friend avoids discussing your former partner maybe because she is harboring some feelings for him that she does not what to divulge to anyone.