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A person's love is as deep as the sea.
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Deep friendship
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Dedicate oneself wholeheartedly to friends or others.
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Intimate/intimate/intimate friends
Idioms that express deep friendship include "Eight Worshiping Friends", "Going with White Call", "Being a bosom friend", "Being affectionate and righteous", * * * Quenching thirst by drinking poison, meeting each other late, never leaving, friendship in the arm, and gentle friendship.