backslid
/ˈbækˌslɪd/Definitions
1. verb
to fall away or regress from a particular standard, practice, or condition, especially after a period of improvement or adherence.
“The church leader was disappointed to see that many of its members had backslid and resumed their old habits.”
2. noun
an instance of falling away or regression from a particular standard, practice, or condition.
“The pastor’s sermon was about the dangers of backsliding in one’s faith.”