back·slide
 /ˈbækˌslaıd/  verb  , -slides, -slid /-ˌslıd/ , -slid·ing [  no obj  ]
  : to start doing something bad again after you have stopped it
   I was afraid of backsliding [=relapsing] into my old habits.
   Smokers who quit often backslide within a year.
  back·slid·er /ˈbækˌslaıdɚ/  noun  ,  pl   -ers [  count  ]