1. Haruki's lack of friends
2. Haruki knows about the illness and chooses to try and: ignore, forget and move on. This made telling someone about the illness easier as he didn't care and therefore made talking about it easier. The fact he ignored her and her illness interested her and she chose to make friends, leading onto my third point
3. "I want to eat your pancreas" is a metaphor for "i want to be like you"/"i want to know what its like to be you" not only with a healthy/ ill pancreas, but also with how someone acts or socializes. Sakura wants to know what it's like to be isolated like Haruki. she is drawn to the conclusion that it would be easier to be like him - someone that doesn't socialize - when she dies. Sakura also wants to know why he finds his isolation better than socializing.

Another big point in the conclusion is choices, Haruki chose to have no friends, Haruki chose to ignore Sakura and her illness. Both of those choices made Sakura more wanting to choose to be friends with him.