Faithless

Not believing; not giving credit.

Not believing on God or religion; specifically, not believing in the Christian religion.

Not observant of promises or covenants.

Not true to allegiance, duty, or vows; perfidious; trecherous; disloyal; not of true fidelity; inconstant, as a husband or a wife.

Serving to disappoint or deceive; delusive; unsatisfying.