Nicole Kidman's tried to fly under the radar in Tennessee Thursday after a rough week that saw her file for divorce from Keith Urban ... but she couldn't escape the camera lens of the paparazzi. We broke the story ... Nicole and Keith have been living apart since the beginning of the summer -- with Nicole watching their two kids. Nicole filed for divorce on Tuesday ... and, the two have a parenting agreement in place already that we've seen. Our sources say Kidman wanted to keep her marriage to Urban going ... but, he was ready to move on from their relationship. Sources in their inner circle say they suspect Keith is going through a midlife crisis.