faithfulness       
noun [ U ] uk/ˈfeɪθ.fəl.nəs/ us/ˈfeɪθ.fəl.nəs/
 忠诚,忠实
the quality of being faithful to someone or something
  The priest stressed the importance of faithfulness in marriage. 牧师强调了婚姻中忠诚的重要性。 
 Synonym: fidelity
Opposite: infidelity