Fiel vs. leal
The Spanish words fiel and leal both translate to faithful or loyal in English, but are used in slightly different contexts.
Fiel
B1Fiel usually refers to faithfulness or loyalty in relationships, particularly marriages.
Ella es fiel a su marido.
(She is faithful to her husband.)
Ser fiel no es una obligación, es una elección.
(Being faithful is not an obligation, it is a choice.)
Leal
B1Leal, on the other hand, often refers more to loyalty in a broad sense, such as loyalty to one’s friends, country or principles.
Los soldados fueron leales a su país hasta el fin.
(The soldiers were loyal to their country until the end.)
Los amigos leales son un tesoro.
(Loyal friends are a treasure.)
Summary
Fiel and leal both indicate a sense of loyalty and faithfulness. However, fiel is more used in personal relationships scenarios while leal tends to be used in broader areas such as one's loyalty towards their friends, country, or personal convictions.