The Character of Medea can be seen as many things. I believe Medea is a crazy woman that cares a lot and and solemnly about Jason's betrayal. She is hurt of what he wants even when it comes to him asking her to be his mistress, and when he tries to explain what happened, she is still bothered. She goes on trying to hurt Jason, and i feel she is just made of pure evil, that there is no question about her evilness.
Medea has a problem, maybe a mental problem, an obsession with Jason may be the correct wording for it. She kills her kids not for any other reason, but to hurt Jason. She also tries to poison Jason's wife. She shows makes Jason see all of his loss and then she leaves, as if the victim of what happened. Yet indifferent of what happened she is the only one to blame, because as much as a betrayal could hurt, she went to an extreme. To kill another being, not just one, but several, or even to kill those who have your own blood, who she gave birth to, its all simply inhumane.