Though his marriage was already in trouble in the Pilot, he split with Sheila before work one day when he found Karen under the table, giving Ian Gallagher oral sex. Ian and his brother Lip quickly escaped the house but Eddie later showed his anger by attacking their father and telling him to pass the message along. Later on, Eddie finds Frank again and apologizes for the attack with the two talking over his failed marriage but his talks about Sheila’s financial benefits cause Frank to visit her.
Eddie appears to be quite religious, which causes his break-down when he learns of Karen's true sexual nature. After leaving his own home, he moves into the basement since he could afford to support his family or live with his brother.
In Casey Casden, Eddie talks with Frank about his relationship with Sheila and says Frank is in for it with Sheila's deviant sexual acts. Late at night, he advises Frank to take the pain pills now after seeing Sheila preparing her tools.
As of But at Last Came a Knock, Eddie reaches frustration with Karen and ends up making a deal with Karen to go to his church's purity ball, in hopes of getting her to stop having sex. She agrees to go in exchange for a car. Karen accepts the deal, to his relief.
During Nana Gallagher Had an Affair, he is confident in changing his daughter. He also tells Sheila to give up on Frank who went home after his wife came back. Eddie appears to get on better standing with his family, as he takes a picture with his daughter and has a dinner with them. He and Karen even have fun together at the dance, almost reconciling but he ends up calling his own daughter a whore and rescinds the car offer when she admits her sexual history at the ball (a required part of the purity ball's program). After this, they go home where an upset Karen vandalizes Eddie's room. His actions also give an angry Sheila strength to not only go outside but force Eddie out of their house whilst Eddie is wallowing in self-pity feeling that Karen had disgraced his reputation.
In Daddyz Girl, hell bent on revenge after being shown up at a religious parent and child meeting, Karen has sex with an unwilling Frank and films it as well as posting various other hate filled blogs directed at him.
Feeling angry, Eddie pursues Frank with a shotgun but is unable to locate him. Later on, he feels that he has failed as a man and throws himself into frozen water while tied to a cement block. Sheila was left to think he was just missing and spent most of her time looking for him.
When his body is found, Frank is questioned, but later released only to find out his attempts to get Eddie's life insurance had failed as the money had been given to Karen.
Karen later urinates on his grave, as a final revenge for him calling her a whore.