what causes pips fear when they stop for the night? how do readers learn that his fears are justified?

Is it ch 53 you mean? The night is dark over the marsh; in the sky the moon is a deep red. Thick mists surround the limekiln to which Pip travels. He enters an abandoned stone quarry and suddenly finds his candle extinguished; a noose is thrown over his head in the darkness. He is bound tightly, and a gruff voice threatens to kill him if he cries out. A flint is struck, its flame illuminating Orlick’s wicked face. Sure, Orlick is a nasty guy out to get him. Pip knew this.

Pip worries someone is following them

no when pip, Magwitch, Startop and Herbert set off for their journey and they stop for the night at that disgusting inn. i didn't understand why he had fear other than it was a nasty place.

Oh, at the filthy inn where they stop that night, a servant tells them of an ominous boat he has seen lingering near the inn; Pip worries that it could be either the police or Compeyson.