Opposite words for loyal:
faithless, irresolute, unpatriotic, mutinous, uncertain, treasonable, capricious, hesitant, wavering, seditious, unfaithful, renegade, false, disloyal, dubious, irresponsible, undependable, insurgent, fickle, subversive, dispassionate, recreant, inconstant, untrue, traitorous, perfidious, faltering, rebellious, untrustworthy, treacherous, shaky, uninterested, vacillating, treasonous, apathetic, unreliable.
Usage samples:
  1. A really loyal servant should do nothing for which he is not prepared to answer, even though his master desires it.
    "The Constitutional History of England From 1760 to 1860", Charles Duke Yonge.
  2. Afterward I learned that he was our dragoman's father; but I was loyal and did not tell.
    "It Happened in Egypt", C. N. Williamson A. M. Williamson.
  3. He was loyal to no one, was Philip, not even to his father.
    "Richard Carvel, Complete", Winston Churchill Last Updated: March 5, 2009.
  4. That unalterable code again,- the religion of being loyal to one's brand.
    "The Settling of the Sage", Hal G. Evarts.