The only thing I can think of is that the word is repeated for emphasis or dramatic effect. The person has some emotion attached to "leaving" perhaps wonder or sadness or surprise. Here is a stanza from "The Highwayman" Note the repetition of "riding" for poetic effect: And still of a winter's night, they say, when the wind is in the trees, When the moon is a ghostly galleon tossed upon cloudy seas, When the road is a ribbon of moonlight over the purple moor, A highwayman comes riding— Riding—riding— A highwayman comes riding, up to the old inn-door.
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