Polybus was nothing to you, that’s why, not in blood
Oedipus' fatal flaw is when he kills his father as the prophecy said. This event kills his father, eventually leads to death of Jocasta, and Oedipus stabbing his own eyes.
Why should I have eyes? Why, when nothing I saw was worth seeing?
When Oedipus hears about the prophecy, he does not want it to become true. His hubris allows him to believe that he can define the gods and their prophecy.
Oedipus is awaiting news from the messenger about his relationship to Polybus. The messenger instead reveals that the prophecy came true, causing a massive change in events.
What spasms athwart me shoot, What pangs of agonizing memory?
Oedipus discovers all the damage he has done when he sees that his wife/mother has committed suicide. In response to this discovery, Oedipus stabs his eyes out with the needle from a pin.
When Jocasta finds out that she is married to her son, she kills herself. This is a catastrophe because not only is it the death of Jocasta, but it leads to Oedipus blinding himself, leading to a new king.
Oedipus and Jocasta are shocked upon finding out that the prophecy came true. This is the catharsis because the audience becomes emotional, and this leads to a "rebuilding" of the kingdom.