apostate

betrayer, double-crosser, quisling, traitor, traitress (or traitoress), turnabout, turncoat

abandoner, come-outer, dropout, leaver

defier, insurgent, insurrectionary, insurrectionist, mutineer, rebel, red, revolter, revolutionary, revolutionist, revolutionizer

discontent, malcontent

recusant, refusenik (also refusnik), refuser

accommodationist, collaborationist, collaborator, sellout, subversive, subverter

coconspirator, conspirator, intriguer, plotter, schemer

defector, deserter, renegade

blabbermouth, gossip, gossiper, gossipmonger, informant, informer, rat, rumormonger, snitch, snitcher, squealer, stool pigeon, talebearer, talker, tattler, tattletale, telltale