Friend?

Far away in a land like ours
live some people with ordinary powers
they look like us and so do eat
but alas, we can never meet!

We used to live together earlier
unless somebody did us apart
my grandpa tells me he misses his friend
a person who then had to depart

One day he set out to meet him
but he did not ever return
papa says he is staying with them
reliving his childhood and having fun.

I asked him when will he return
to which he never replied,
But what I am still wondering is  
Why did papa had to cry?