the.com/apple of my eye

means The person or thing cherished above all others — a term of deepest affection and pride.

from The 'apple' here originally meant the pupil of the eye, which people once believed was a solid, apple-shaped sphere — so 'apple of the eye' meant the precious, vulnerable core of sight itself, something you'd guard fiercely. The phrase appears in Old English (as 'æppel' for the eye's pupil) and shows up in King Alfred's writings, later entering the King James Bible, which cemented it in everyday English. Losing your 'apple' meant losing your sight, so calling someone your apple meant they mattered as much as the ability to see.