Loyal means to do your best for an idea, person or organization, not to betray it. Someone who is loyal does not do anything that will harm the thing to which they are loyal.
"I am very loyal to my employer."
"My neighbour is loyal to the community."
"If you will be loyal to me and the company, I will look after you."
Faithful is slightly more than loyal. It implies the continuous and unbreaking nature of the loyalty. You may be loyal to your employer while you work there, but not once you have left. Faith is also used in a religious context.
"My dog is so faithful, I love him."
"I have been faithful to God and his teachings all my adult life."
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