Follow the relationship between pi and richard parker. They endure over two hundred days of hardship together, but in the end, Richard Parker leaves and Pi feels abandoned. Why is this significant?

During their months together at sea, Pi formed a bond with the Bengal tiger. Pi never forgot that Richard Parker was a 450-pound carnivorous beast, and they never were on friendly terms. Yet in some ways, Pi came to consider Richard Parker his friend. He credited the tiger with keeping him alive, because a person needs meaningful work and a purpose, and Richard Parker provided those things for Pi. Keeping the tiger alive (and satiated) helped Pi survive because it stopped him from going mad or giving up hope and succumbing to despair.
When they finally come to land in Mexico, as Pi is looking toward shore and assessing how far out they are, Richard Parker leaps over him and into the water. From there, the tiger runs onto the beach. He runs one direction first, then turns around and runs the other direction direction along the beach for a while before veering into the jungle. Pi never sees him again. Pi is certain that Richard Parker will look his way and make eye contact, perhaps even growl goodbye, but he doesn't acknowledge him in any way. Pi was hoping that the tiger would do something that "would conclude our relationship." Humans who have spent much time together don't go their separate ways without some sort of parting ceremony. But Richard Parker's actions show that he was, after all, an animal without a concept of human sentimentality or ceremony.
This is painful for Pi because he had grown to appreciate the tiger and had in many ways sacrificed his own wellbeing and comfort for him. For example, when Pi realized the algae island was carnivorous, he could have abandoned Richard Parker on the island, leaving the tiger to die, which would theoretically have made the rest of his journey safer and less complicated. But he waited for Richard Parker to return before he sailed away from the island. Such altruistic acts cannot be reciprocated by animals, especially an undomesticated creature like Richard Parker. As a zookeeper's son, Pi knows that animals are not humans, but spending so much time with Richard Parker as his only companion made Pi come to value the tiger as more than just an animal. Richard Parker's abrupt and unceremonious parting drives home the reality of how one-sided their relationship had been.