Is he is the apple of my eye a metaphor?

Yes, the phrase "the apple of my eye" is a metaphor. When someone is referred to as "the apple of your eye," it means you treasure and adore them very much. It's a figurative way of expressing strong affection and a great fondness for someone. The metaphor compares the cherished person to the prized, delicate center of an eye - the pupil, which is considered precious and deserving of utmost attention and care.