The star, who was discovered by music manager Scooter Braun when he was 13, admitted to heavy drug use and abusing his relationships.
"I became resentful, disrespectful to women and angry," he wrote.
"I became distant to everyone who loved me... I felt like I could never turn it around."
The Canadian star, who has been candid about his mental health struggles, explained how the constant praise he received in his teens had distorted his perspective on life.