We kick off 2 Samuel with David "mourning" for his dead "friends" that he "didn't have killed".
And actually immediately we start with a completely different version of how Saul died. Which kicks off the bullshit parade of David being absolutely perfect and having no malice for his enemies who just happen to keep dropping dead as soon as he leaves the room.
It turns out Saul had another son who didn't die on the battle field, named Ishbaal. We start seeing Ishbaal wasn't really the fighting type, at least as far as the writer wants us to think. But while David is crowned king of the southern kingdom of Judah, Ishbaal is crowned king of the the northern kingdom of Israel.
But it doesn't take long for Abner, Saul's commander, to turn on Ishbaal. Which works out great for him. Also, David demands to have his first wife, Ishbaal's sister, returned to his possession and she is, much to her current husband's lament.