The true prophet was identified with the false, as the true religion of Jehovah was being identified with the new idolatrous religion of Jeroboam. It was probably only another effort to confuse the minds of the people so that they might not perceive the seriousness of the issues at stake. The disobedience of the prophet was playing into the hands of wickedness.
His own grave.
Probably as a token of remorse and personal compassion for the victim of his own treachery. Burial in Palestine was often in rock-hewn tombs where families might be buried together.