I want to eat your pancreas

The protagonist is a bookworm whose world only revolves around books and doesn't care much of the world beyond it. He is uninterested in a lot of things and believes no one has any interest in him as well. When he sees a handwritten book titled "Living With Dying," he assumes it as a secret journal belonging to his famous and cheerful classmate named Sakura Yamauchi. She then shares to him about the pancreatic illness she's suffering from and she might die anytime soon. Only her family is knowledgeable of her illness and not even her closest friends are aware of it. However, he shows no interest or sympathy for her, but ends up accompanying her for the rest of her days.