Faithfulness is commitment to someone or something. Faithfulness is especially valued in spouses and in sports fans.
When a married person is faithful, they stand by their spouse and don't cheat. Faithfulness refers to this quality of being faithful and loyal. A patriotic person is full of faithfulness to their country. Someone who works at one company for decades has faithfulness to that company. People can have faithfulness to ideas too, including religious, political, and artistic ideas.