8 God is repaying you for killing Saul's family and stealing his kingdom by giving your kingdom to your son, Absalom. You are caught in your own mischief. You are a bloody man.
Ahithophel's plan won't work because David and his men are mighty men.
11-12 Hushai proposed another plan. He said to Absalom,
Gather all of Israel together and then attack David, leading the battle yourself.
That way you will kill David and all of his men.
Hushai's plan is accepted (so God could bring evil on Absalom)
14 Absalom and all the men of Israel said, "Hushai's plan is better than Ahithophel's."
God made Absalom reject the advice of Ahithophel so that he could bring evil on Absalom.
David is warned
15 Hushai said to Zadok and Abiathar, "Go warn David about Absalom's plan."
17 Zadock and Abiathar sent their sons to deliver the message to David.
Ahithophel hangs himself
23 When Ahithophel saw that Absalom didn't follow his advice, he hanged himself.
Ahithophel hangs himself by Rudolf vom Emns
24 Absalom and all the men of Israel crossed the Jordan in pursuit of David.
A few more words about this episode
Ziba, the servant of Jonathan's son, Mephibosheth (16:1)
In episode 121 (2 Samuel 9), David said he'd be kind to Mephibosheth, for Jonathan's sake.
Absalom raped his father’s ten concubines (16:22)
In episode 123 (2 Samuel 12:11), the prophet Nathan told David that God would punish him for the Bathsheba/Uriah affair by forcing his "neighbor" to have sex with his wives in front of everyone. This is the fulfilment of that prophecy, with Absalom being the "neighbor."