What do we learn from "v'Libi Chalal b'Kirbi"?
Brachos 61b: Tzadikim are ruled by their Yetzer Tov. (Rashi 61b - David said, it is as if I have no Yetzer ha'Ra, for I can overcome it.)
Bava Basra 17a: The Yetzer ha'Ra did not rule over him 1 , just like it did not rule over the Avos.
Shocher Tov: Sin makes the Nefesh like a Chalal (Mes).
Radak: My heart was killed inside me amidst my great afflictions.
Malbim: Above (16), it says that they chased "Oni v'Evyon v'Nich'e Levav." David says, I am Oni v'Evyon, and v'Nich'e Levav, for my heart is hollow inside me.
Avodah Zarah 4b: David was not apt to sin with Bas Sheva (had Hashem not made such an overwhelming temptation). He caused David to sin to teach that repentance of an individual is always possible.
