backslide

Short definition from Wiktionary

Verb

1. 1
   To regress; to slip backwards or revert to a previous, worse state.
2. 2
   To shirk responsibility; to renege on one's obligations or commitments.
3. 3
   To revert back into a life of sin after being saved.

Noun

1. 1
   A backward regression; a reverting back to a worse state.
2. 2
   A dance move in which the feet are alternately slid back and the heels lifted, giving the illusion of walking forwards while actually moving backwards.