Malbim: Avshalom really did seek to kill David, and David's sons and wives. He would kill his father and brothers and rape the wives, in order to establish his kingship, like he began via raping the Pilagshim. "Your servants saved your life, and your sons' lives" - how are you sad over Avshalom's death?! If he were alive, you and your sons would be in danger. They killed him to save you, like a Rodef! Also refer to 19:7:1:2, 19:7:2:1, 19:7:3:1.