I would propose that The Age of Innocence is not a love triangle or a romantic tragedy. It is rather a study of one young man whose basic problem is neither romantic nor erotic but basically political.
Archer sees the glamorous Countess Olenska as an escape from his foreordained life, a life devoted to maintaining his own social milieu and class. Because the countess has broken Society’s rules and is on the verge of banishment, running away with her would foreclose the role that is expected of Archer and would open vague alternative possibilities for him.