The most suspenseful part would be (spoiler alert) when Alaska passed away in a car crash. She almost forgot about her 8th month anniversary with her boyfriend. Thus she rushed to his house by car although she was drunk. The main character, Miles, had to deal with his emotions after finding out that she passed away the next morning. With his good friend, "Colonel" , they decided to find out how she crashed. They did not know if it was really an accident or she committed suicide. They were also guilty as they did not stop her from going to her boyfriend's house when she was drunk.
They decided to give up on the mystery and come to terms with their loss and move on. They eventually decided to focus on their studies instead.