So the civil a=war between Abner/Ish-bosheth and David continued with David growing stronger and Abner growing weaker.
David's wives started having babies. (6 babies by six women, I think,)
Abner has sex with Saul's concubine and Saul's son accused him of doing it to claim the throne. Abner did not like that accusation.
Abner decides to covenant with David now and David agrees if he can have his first wife back. This happens (woefully) and then David and Abner come to terms.
But Joab, David's commander murders Abner in the meantime, because of what Abner did to Joab's brother.
David did not take it well. Hebron was a city of refuge and even a blood avenger could slay without a trial there (Ryrie), so even though Joab felt justified, David did not. He severely cursed him and his whole family- even though it was his nephew. David pointed out that Abner was a prince of the first anointed king from God. (Saul's relative.)