Poseidon was an older more powerful deity. She knew that he was a serial philanderer and couldn't do anything about it. She believed Medusa breaking her vow of chastity or just violating her temple was the most egregious of the sins performed.
The Medusa we know was raped by Poseidon in the goddess Athena's temple. Athena then punished her for desecrating her sacred space by cursing Medusa with a head full of snakes and a gaze that turns men to stone.
Medusa and Poseidon engaged in a love affair and would have two children together, but not before Athena discovered the illicit affair. When Athena discovered the affair, she was enraged and immediately cursed Medusa by taking away her beauty.
“Instead of punishing Poseidon, Athena turns her rage against Medusa, on the one hand because she is not able to punish the powerful Poseidon, and on the other hand because she is envious of Medusa´s beauty.”
In fact, Athena was jealous of Medusa's beauty and lustrous hair. Poseidon ravaged her and took what she held dearly, her purity. Athena, outraged by this incident, cursed Medusa and turned her wonderful hair into venomous snakes, her beautiful face turned so ugly that any man who gazed upon would turn to stone.
In fact, she was gorgeous and attracted the attention of the sea god Poseidon. There was a problem though; Medusa had taken an oath of chastity in order to serve the virgin goddess Athena in her temple. Instead of taking no for an answer, Poseidon brutally attacked and raped Medusa inside of Athena's temple.
Athena and Poseidon entered into a contest to be the patron of Athens. Poseidon produces a spring of water but it was salty. Athena bested Poseidon by producing an olive tree on the Acropolis. Poseidon also raped Medusa—a mortal who had the reputation of being beautiful—in Athena's temple, desecrating it.
When Medusa had an affair with the sea god Poseidon, Athena punished her. She turned Medusa into a hideous hag, making her hair into writhing snakes and her skin was turned a greenish hue. Anyone who locked gaze with Medusa was turned into stone. The hero Perseus was sent on a quest to kill Medusa.
According to Apollodorus' version of the myth, Athena was angry with Medusa because she had claimed to be more beautiful than the goddess. In both cases, however, the result was the same. In the end, Athena turned Medusa into a figure of horror, a Gorgon with venomous snakes instead of hair.
Medusa was not cursed, she was actually helped by Athena. Her patron goddess gifted her with an ability that would never let Medusa feel powerless again.
There is a version of Medusa's story that states she was cursed by Athena as a punishment for being raped by Poseidon in the temple. As Athena could not confront Poseidon, she held Medusa accountable for bringing dishonor to her temple despite the fact that it was not her fault.
First of all, Athena is in no position to punish Poseidon, whatever his crimes. She can outsmart him, as she has done before, but punishing him is way out of her reach. The only god that could do such a thing would probably be Zeus.
She was affected by the evil's, becoming greedy and ambitious to rule the world after the destruction of the Greek pantheon. She could have been jealous of Zeus' authority over the world, which would also explain why she wanted Kratos to kill him.
One day, Poseidon (or Neptune), the God of the Sea and rival to Athena, saw Medusa and was mesmerized. But Medusa being a loyal priestess to the Goddess rejected him.
The Moral of Medusa
This myth is actually a warning to mortals. Don't believe yourself to be equal to the gods. Who was Medusa to reject the advances of Poseidon? A mortal should never do this.
Instead of punishing Medusa with a head of snakes that could turn men to stone, Athena protected her. Athena blessed Medusa with the ability to defend herself, and her daughters, from men. So she would never be hurt again. But to the male Gods around Athena, this was punishment enough.
Medusa was very proud of her beauty and thought or spoke only of herself. Each day she boasted of how pretty she was. Medusa even boasted that she was prettier than Athena, goddess of wisdom, who watched over Athens. Athena decided to punish Medusa for her pride.
Once he found her, Perseus went up and cut off Medusa's head while she was sleeping. However, when she was killed, Medusa was still pregnant from her liaison with Zeus.
In another version, she was cursed by Athena, for having consensual sex with Poseidon in the temple.
She stated that Zeus' death was necessary if humanity was ever to be freed, and would aid Kratos throughout his quest. Athena aiding Kratos in Astral Form in God of War III.
Poseidon warned Kratos that Olympus' destruction meant the world's destruction. The Ghost of Sparta did not react and told him to prepare for his own death, Kratos proceeded to brutally beat on the sea god, before finally finishing Poseidon by gouging out his uncle's eyes with his thumbs and snapping his neck.
In a late version of the Medusa myth, by the Roman poet Ovid, Medusa was originally a beautiful maiden, but when Neptune (the Roman equivalent of the Greek Poseidon) had sex with her in Minerva's temple (Minerva being the Roman equivalent of the Greek Athena), Minerva punished Medusa by transforming her beautiful hair ...
Athena was an armed warrior goddess. The Parthenon at Athens was her most famous shrine. She never had a true lover or someone to hug and hold her; all she had was her loving mother, caring father and most of all her brothers and sisters.
In Greek mythology, the goddess Athena is immune to romantic love, so there is no particular lover for her.
According to legend, Athena became the patron goddess of the city of Athens after a competition with Poseidon, though he remained on the Acropolis in the form of his surrogate, Erechtheus. After the fight, Poseidon sent a monstrous flood to the Attic plain to punish the Athenians for not choosing him.