Answer:
Percy feels guilty about Grover getting into trouble. Percy left Grover even though he promised that he would wait for Grover to get out of the bathroom once they got off the bus. Percy also probobaly feels bad about Grover having to come to their cabin in the middle of a rain storm. Plus, Percy got Grover hurt. Not intentionally, but his choices got him, Sally, and Grover into a car accident when being chased by the minotaur. If Percy would've listened then Grover would have been given a searcher's lisense and would'nt be hurt.
(The Lighning Theif or book one of Percy Jackson and the Olympians)
Hope I helped!!
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