What does 1 Samuel 29:8 mean?

David said to Achish, 'But what have I done wrong? Have you found anything against me since I've been with you? Why can't I go fight your enemies with you?' 1 Samuel 29:8 - Modern Text Bible

(David protests, acting surprised and hurt, though he may be relieved. He wants to keep up appearances with Achish, even though fighting Israel would put him in a terrible position.)