Athena loved to admire herself and look at herself in the mirror. This was because she was considered the most loveliest or prettiest in the city.
Medusa always believed that she was truly the most loveliest and prettiest girl in her city. She would always brag to people about how bright here hair was, how green her eyes were, any much much more.
Here, Medusa is telling her worshippers to not have any contact with men.
Although Medusa told her worshippers not to have contact with men, Medusa herself had a contact with a man named Poseidon. This meant that Medusa was having an affair with Poseidon.
Medusa or Poseidon did not know that one of Medusa's worshippers had caught Medusa having an affair with Poseidon. Later on the worshipper ran off to tell Athena that Medusa was having an affair.