1)
What is the meaning of "Lev ha'Melech Al Avshalom"?
1.
Radak: He desires Avshalom.
2.
Malbim: He still bears resentment.
2)
If Yo'av knew what David feels, why did he not directly talk to him?
1.
Radak: He inferred from his words [that he desires him], but he was afraid to say so explicitly.
2.
Malbim: Even though David ceases to pursue him, Yo'av knew that he still bears resentment.