There were a few contenders for my best shot: the shot of Tom hiding behind a mirror as his head pokes out the top and Dickie's body is reflected in his place. Another of Tom, after he decides that it's too dangerous to impersonate Dickie anymore, and his reflection in the top of the piano begins to morph and pull apart to become two separate entities again. But, I knew what shot I was gonna pick even before I rewatched the film. As Tom and Dickie (Jude Law in his star-making performance) make their final trip together (and Dickie's final trip ever) on the train to San Remo, Tom senses that the end is near for his new way of life and the relationship he has formed with Dickie. As Dickie sleeps, Tom lightly paws at the man's expensive suit jacket, breathes in his scent, and then adjusts his head so that the two men's reflections conjoin:
Unlike the other images mentioned, I chose this one because it captures the sexual nature of Tom's infatuation with Dickie. This is the closest that Tom will get to becoming one with the flesh and blood Dickie. Dickie's charisma gives off an omnisexual power. It's not that he intentionally leads Tom on (especially in that bathtub chess scene) in a way that promises sex to the confused Tom. It's that he wields his sexuality as a power over people. Dickie likes being lusted after and Tom is very much susceptible to it. And it plays with Tom's mind. He's not sure if he wants to be Dickie or be with Dickie. As he looks at their reflection–leaning in with his mouth slightly opened as if going for a kiss–his lust is caught up with the image of them together. The reflection capturing his mix of desire and envy.