Is this quote in Curly Sue?

No, that's not from Curly Sue. I think you're thinking of What's Eating Gilbert Grape. The line "It's not goodbye, it's goodnight" is used frequently in that movie.

Im sure thats used in The prince of Bel Air episode

I remember that quote being from John Q. He tells his son to always say "it's not goodbye, it's I'll see you later".