He began to keep a journal and was 'faithful to' it for years. [=he continued to write in his journal for many years]
The movie is 'faithful to' the book. [=the story told in the movie closely matches the story told in the book]
He was not 'faithful to' his word. [=he did not do what he said he would]
(..) Why shine it here? Jayd has been declared a hostile world. I can't help but wonder who's responsible. RUBYN: I'm just a faithful son. I honor my family, I follow the Golden Dragon... ...while you have other loyalties. Not loyalties. Duty. (..)2011 Green Lantern: Emerald Knights