Separatist

(n.) One who withdraws or separates himself; especially, one who withdraws from a church to which he has belonged; a seceder from an established church; a dissenter; a nonconformist; a schismatic; a sectary.

Thesaurus Entries

abjuratory, apostate, backslider, bolter, breakaway, collaborationist, collaborator, convert, defector, demurrer, deserter, dissenter, dissentient, dissident, fifth columnist, misbeliever, mugwump, mugwumpian, mugwumpish, nonconformist, objector, opinionist, opposition voice, proselyte, protestant, protester, quisling, recidivist, recreant, recusant, renegade, renegado, renegate, renunciative, renunciatory, repudiative, repudiatory, reversionist, revocatory, runagate, schismatic, seceder, secessionist, sectarian, sectary, strikebreaker, tergiversant, tergiversator, traitor, turnabout, turncoat, turntail