At first it seems like it'll be alright. Eddie agrees to let his niece go to work. Catherine's future isn't shaping up to be exactly what Eddie wanted, but he can live with it. Marco and Rodolpho arrive from Sicily. They look forward to carving out a new life in America. However, when Catherine and Rodolpho start to date, Eddie's unfortunate obsession rears its ugly head.
Unlike the dream stage in a lot of tragedies, there's never a moment where it looks like Eddie is going to get what he wants. Eddie commits to a course of action, sure, but everything he tries immediately fails.
Eddie does all kinds of stuff to try and pry the two apart. He plants seeds of doubt in Catherine, goes to a lawyer, and eventually forces kisses on both Catherine and Rodolpho. His tactics become more and more desperate with every failure.
Eddie really screws up his life when he turns in Marco and Rodolpho. After Marco calls him out publicly, everybody in the neighborhood thinks he's a complete jerk. Beatrice hates him. Catherine hates him. Everybody hates him. To make matters worse, it doesn't even stop his niece's relationship. Catherine and Rodolpho plan to get married just so Rodolpho won't get deported. It really is Eddie's worst nightmare. He's lost everything he ever loved or hoped for.
Beatrice basically tells Eddie that his real problem this whole time is that he has incestuous feelings for Catherine. Eddie just can't deal with that. The idea turns him into a total maniac. When Marco challenges him, he runs downstairs, frothing at the mouth, only to meet his death. In classic tragic style, the hero's fatal flaw causes his own destruction.