How does the horse serve as a true friend and companion to Iona?

The horse serves as a true friend and companion to Iona because his fellow human beings were indifferent to his sufferings. After his alienation from the society, he began to confide in his horse who listened silently without judging him like a true friend. His desperate attempts at communication had failed so he discussed his whole story to the horse, feeding it hay, saying that he wishes that his son was still alive to support him in his old age.