Yoongi had a good relationship with his mother. When he was 15, his whole house burned down. He became overcome with emotion, and dissociated from the moment. He tells himself his mother wasn't inside when it burnt down, but he knew it wasn't true. It created so much trauma within him. Him telling himself that his mother wasn't there makes him blame himself for her death. It did not help that Yoongi's father didn't take him to any form of therapy. His father did not know how to replace the lost bond that he had wiht his mom, and so Yoongi did not want to make connections and bond with others. Yoongi's connection to his piano helped him.
When Yoongi was expelled from school, he went to look for the keys to his moms old piano. He throws them away, as a way to get rid of his anger at being expelled from school. The action of using the keys for his anger about the school and protecting Jungkook links his relationship with his mom and the relationship with Jungkook.
Yoongi also has a drinking problem. He acts out in fights, to get rid of all the anger and trauma. He self-medicates and self harms, the latter often similar to Taehyung getting in fights.