I’ve been there before.

apostasy (a·pos·ta·sy): / uh PAHS tuh see /
noun

(1) a rejection of, departure from, or renunciation of one’s religious faith
(2) the abandonment of a previously held loyalty, as of a political party, cause, principle, religion, or allegiance; desertion; defection

[From Middle English ‘apostasie,’ possibly from or via Old French, from Late Latin apostasia meaning “defection,” from Greek apostasis meaning “standing away, revolt, withdrawing,” from aphistanai meaning “to revolt,” from histanai meaning “to stand, to place.”]

Usage: My religious apostasy occurred nearly two decades ago.