1)
Why did he tear his garments?
1.
'Rashi': He heard "Hashem will take you and your king that you put upon yourself [to exile]" (Devarim 28:36). He expounded, "that you put upon yourself" [refers to himself] ? the nation made him king. It was not via a Navi according to Hashem's word.
2.
Radak (Melachim II, 22:11, from Yuma 52b): The Sefer was rolled to the curse "Hashem will take you and your king? [to exile]" (Devarim 28:36). It hints to the exile of Shomron, Yehudah and Melech Yehudah.
