Who is eurlylochus and why does he not enter circles castle

He is portrayed as an unpleasant cowardly individual who undermines Odysseus and stirs up trouble. He also was the husband of Odysseus's sister, Ctimene. He doesn't enter the circle castle because he Only Eurylochus, who suspects treachery, does not go in. He escapes to warn Odysseus and the others who have remained with the ship.