He fell unto me - The regular word for deserting and going over to the other side. See Jeremiah 37:13; Jeremiah 38:19.
Related Commentaries of 1 Samuel 29:3
1 Samuel 29:3
3 Then said the princes of the Philistines, What do these Hebrews here? And Achish said unto the princes of the Philistines, Is not this David, the servant of Saul the king of Israel, which hath been with me these days, or these years, and I have found no fault in him since he fell unto me unto this day?