Chapter 153- Past With A Smile (Part 1)
Ever since young and after the accident that happened to his father, he had seen how ugly a human heart can be if put in the right situation and time.
The friends he thought were the most important part of his life quickly turned on him and exiled him from their lives at the first mistake he did. They destroyed his life and made him the laughingstock of many and the target of mockery and insults from many more.
Since then, Rin had this doubt seeded into his heart that no one in this world was actually good except for his family. It was a debatable thought process that could only apply to those who actually experienced it firsthand. That's also the reason why when the last friend Marcus he had didn't leave him at all, he felt as if he was the only person other than his family that was good.
Maybe it was also the reason for Rin to keep on following him even when he made gruesome mistakes that affected Rin himself.