I've been trying to think of how to describe what I am thinking, but it keeps coming out wrong.
It's a crazy kind of love, to love an orphan. You pour your heart out to a child with no family; no dad to carry them on their back and no mom to read them bedtime stories or kiss their forehead when they're sick. You hold them when they're 2 months old, with such tiny hands they barely fit around your finger. You watch for their first smile, listen for their first word. You nervously prop them up to sit, lure them toward something shiny when they learn to crawl, and hold their hand while they learn to walk. You chase them and sing to them and read to them and make funny faces at them. You know where they are ticklish and which toy is their favorite. You start to love them like you would your own.
Then, just as it should be, they get to go home. And just as it should be, you feel like a piece of your heart leaves with them. Someone else will pick up where you left off and love them for the rest of their life.
The hardest and greatest part is that they'll never know you existed.