1)
Why did he say "you love Ra" and "Sheker"?
1.
Malbim: You cannot say that you erred, and thought that Achimelech is culpable. Why did you love the evil, and tell only the evil, and not the good, that Achimelech did not know anything, and that Bulmus had seized David?
2)
What was the Ra and Sheker?
1.
Radak: He said that Achimelech knew that David was fleeing Sha'ul, and he helped him; he gave to him bread and asked Hashem (for him, via the Urim v'Tumim). Really, Achimelech did not know that David is fleeing. Sha'ul complained that people are helping David, and Do'eg said that Achimelech is among them.
