A Dark Brown Dog by Stephen Crane

A child is standing on a street corner when a little brown dog approaches. They have a friendly exchange, but it quickly turns rough with the child hitting the dog. The boy loses interest in the dog and heads for home. He notices the dog following. The boy beats the dog with a stick. Despite the mistreatment, it's eager to stay with the boy.

Source - https://owlcation.com/humanities/Sad-Short-Stories-Online