What thoughts did the postmaster have when he left? How were his emotions different from those of Ratan?

“The grief-stricken face” of Ratan began to haunt the postmaster when he left for his home. The boat had already left the shore when he felt a powerful impulse to take Ratan along with him. But by then, it was too late:

…the boat had got well into the middle of the turbulent current, and already the village was left behind.

The author comments on the postmaster's feelings—“then he felt a pain at heart…” The pain being referred to could be described as the pain arising out of his sympathy for the “lonesome waif,” or it could also be interpreted as the pain caused by his guilty conscience. He knew very well that if he had taken Ratan along with him, all her worries and sorrows would have ended. Still, he didn't do so.

The postmaster, however, began to console himself with philosophical thoughts:

So the traveller... consoled himself with philosophical reflections on the numberless meetings and partings going on in the world—on death, the great parting, from which none returns.

In this way, he tried to disburden himself of the pang of guilt that tormented him.

On the other hand, Ratan was a parentless girl. She had grown much attached to the postmaster, keeping herself busy doing “odd jobs for him” and looking after him. Moreover, the postmaster had begun teaching her how to read. She enjoyed these lessons, and within a short span of time she had made remarkable progress. Since his posting in the village, she had been happy, as she had found a close companion in him. She didn't feel that lonely anymore.

Therefore, despite her request to the postmaster when he left without her, she was heartbroken.

She was wandering about the post office in a flood of tears.

Unlike the postmaster, “Ratan had no philosophy” to support herself with. Her source of consolation was her hope that he would return to take her along with him.

Ratan’s grief was much deeper and stronger than that of the postmaster’s for several reasons. First, unlike him, she had no family to which she could go and seek the warmth of human affection. Second, she was a young, illiterate girl, without a learned man’s philosophical thoughts to console herself with in this time of acute crisis.

So we see that the postmaster had begun to come to terms with the fate of Ratan, finding himself helpless to alleviate her pain, while Ratan “could not tear herself away” despite her deep grief because “she had still a lurking hope in some corner of her heart that her Dada [the postmaster] would return.”