Complex sentence: Bokomon overheard whst Crusadermon said and promised Koichi that he wouldn't tell anyone but told the other DigiDestined about it which did not involve Koji, because at the time Koichi was talking to Koji and they were out of ear shot.
Split into simpler sentences: Bokomon overheard whst Crusadermon said and promised Koichi that he wouldn't tell anyone but told the other DigiDestined about it. Ironically this did not include Koji, because at the time Koichi was talking to Koji and they were out of ear shot.