Had Madge analysed her relationship with Morty, had she examined it as she ought have, she would have realised Morty didn’t beat her because she did something to make him jealous, Morty beat her to beat her.
But Madge didn’t analyse.
When Madge got involved with Casey and he mentioned that Jack was flirting with her, she didn’t listen to what he said, or think of anything save that he was laying the mat to beat her, so ended the relationship.
It was after Jack made a play and she rejected him, that she realised Casey wasn’t playing jealous, he was making an observation.
It was then she sat down and went over her relationship with Morty and finally realised that he beat her to beat her; it wasn’t ‘jealousy’.
It was then she realised she ended her relationship with Casey for no reason.