When Holden writes a composition for Stradlater we learn about his brother Allie’s death. How you think Allie’s death affected him?

Allie was Holden's brother, he was two year younger than him. He got leukemia and died at a very young age. The night Allie died Holden broke all the windows in the garage and we was only 13 when that happened.
We think it affected him because it seems that they got along really well, and after this tragic event everything started to go downhill for Holden. He started to loose interest in school, his family and even himself.