Moral Obligation Questions

I have been reading the Alexander McCall Smith series about Isabel Dalhousie, who is the editor of a philosophy journal. So her character is constantly pondering questions about morality and what our obligation to others are or should be.

This got me thinking about a hypothetical situation.

What if there were two people, A and B, who were mere acquaintances but who both had something in common, say, collecting rare stamps. These two people were connected by their own choice on a social network.

Then suddenly A loses his rare stamp to a fire, robbery, whatever. A is extraordinarily upset about this circumstance, because this stamp had been an exceptional and difficult acquisition in his collection. Not only is he upset, he makes quite clear his feelings about his situation and specifically what happened to him and which stamp was lost.

B never recognizes the loss of A's stamp. Then a week or so later, B goes on to announce that he has acquired the exact stamp lost by A.

A congratulates B on his good fortune.

However, B still refuses to acknowledge the loss of A, in spite of his own gain. In fact, B goes on posting many stories about the stamp and how it has increased in value, and is even rarer than once believed. At the same time, A has continued to post his feelings about his lost stamp, because it is still weighing heavily on him. Many other of their philatelist friends sent words of regret and solace to A.

So one would assume that the second collector sees at least one of A's posts as they are repeatedly posted.

What is A, who lost his stamp, supposed to do? Should that person "hide" B from his news feed to avoid seeing the stories about the lost stamp? Defriend B completely? Address the person directly regarding the matter?

Meanwhile, what should B do? Are we obligated to have empathy with someone who has lost something treasured, even as we have gained the same? Of course not.

But if B does see A's posts and remains silent, what does that do to B's soul? Is it darker and less than it should be?

Why do people do such things? Should we not strive to be more empathetic to one another?