1)
Why did Yo'av say "if Amon overpowers you, I will go to save"? The other way, he said only "if Aram overpowers me, you will save me"!
1.
Malbim (9): Avishai did not separate from Yo'av, for he expected Amon to stay in their place. (If Avishai sees that Amon leaves, he will go to fight them, and if he needs help, Yo'av will need to go to him.)
