It is clear from the play that Eddie is constantly engaged in creating and protecting his own personal world of illusion where he can remain blind from the significance of his actions and his own true feelings. This is what motivates Eddie: supreme self-interest. Because of the success of his imagined world he never is truly aware of his feelings for Catherine and the only outlet he has for his feelings are invested in suspicion and hatred of Marco and Rodolpho, which causes him to commit completely irrational and unforgiveable acts. It is this that is so tragic about Eddie, and what ultimately causes his tragic end. His inability to recognise and accept the bubble world he has created causes it to turn into a prison from which he is fated never to escape. The irrational actions he starts to "protect" (as he sees it) Catherine from the attentions of Rodolpho then lead to a vain quest to regain his honour by challenging Marco, which ends in his death.
Eddie is a respectable man whom at first had no destiny but after the arrival of the brothers(Marco and rodolfo), his life now has a future. His over-protectiveness towards his neice turned into filial. Eddie's improper sexual desire, that he was unable to hide it from those around him nor from the audience thus losing all sympathy we had towards him, was the reason that had brought him closer to his doom then his self-destruction.
Very interesting question!