Why do some teachers get heartbroken when their favorite student moves to another classroom or move away?

They’re not their friends! One assistant teacher works with a naughty Hispanic little boy but she adores him. We think he’s annoying and all that but she adore him. We like him though. He keeps getting out of his seat, won’t pay attention in class but he’s so smart, he can add, identify things with him and in all. He should be with the older kids since he’s 7 going on 8. He’s too old for the 5-7 year olds classroom. The teacher say he may be the next one to move up a classroom. She’s gotta get him prepared for the next classroom. He should have moved up. That assistant teacher agreed but she looked heartbroken. I mean he NEEDS to move up. He’s in 2nd grade and this class is a kindergarten to first grade class. I’m having a feeling he will move up either in January or next year school year. She was telling me can’t they keep him until May. I was like, “Girl that’s not our decision. It’s the admin decision and parents. He is going to be 8 and it’s too old for this classroom. He needs to move up. Why are you I obsessed with keeping him in the classroom. You’re kind of creepy.”
Some kids are in a level for a short time and they sometimes move them up so our student should move up too.

Why do some teachers get heartbroken when their favorite student moves to another classroom or move away?
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