backslidden
/ˈbækˌslɪdənd/Definitions
1. verb
to abandon or renounce a previously held set of beliefs or principles, especially in a religious context
“The pastor’s congregation was devastated when they discovered he had backslidden into his old sinful ways.”
2. noun
a person who has abandoned or renounced a previously held set of beliefs or principles, especially in a religious context
“The church tried to reach out to the backslidden member and bring them back to the fold.”