Once you've
left "home", you can never truly
return. Moving away from a
parent or parents, whether a
joyful or
sorrowful (or mixed)
experience, is a defining one. After that, you can never re-capture the
feeling you had as a youth in living under a
parent's roof.
Generally refers to the state of flux a person's life gains when entering adulthood. When you return to the place you once called home, thanks to the passage of time, it's probably not going to carry the same connotations as it once might have. The changing of your hometown, the gradual growing apart of old friends, all signifies that fact that the home you once knew is now, for all intents and purposes, gone.