1)
What is the meaning of "Dal"?
1.
Rashi: It is thin, like "Dalos v'Ra'os To'ar" (Bereishis 41:19).
2.
Radak: It is weak, thin and a sad face.
2)
Why does it say "ba'Boker ba'Boker"?
1.
Radak: At night he thought about her and he was awake due to her, and in the morning he had a sad face.
3)
Why did he admit that he was ill due to his desire for Tamar?
1.
Malbim: (a) Yonadav was a great Chacham. He could tell that Amnon was ill due to desire. (b) He needed Yonadav's good counsel.