Some translations set each line of poetry farher to the right than the rest of the text to make it easier to read. The ULB does this with the poetic song in 3:33-34.
David never wanted to hurt Saul's family. Isbosheth criticized Abner and Abner became angry. He decided to help David become king of all of Israel. Abner came and made a treaty with David. As he left, Joab arrived and told him he wanted to talk to him and he murdered Abner. David was very unhappy that Abner had been killed.