what episode of grey's anatomy does derek leave addison for the last time
Grey's Anatomy, Season 3 Edit. In the wake of her divorce, Addison sleeps with Mark. (I Am A Tree). Addison discovers that Derek and Meredith slept together when she finds her panties in the pocket of Derek's tux and struggles with the end of her marriage.ddison and Derek would eventually relocate to New York where they both began their practice alongside Derek's childhood best friend Mark Sloan. Her relationship with Derek eventually becomes strained and she sleeps with Mark.