The self is built upon secrets and the film portrays that in interesting ways. When one forms a relationship, there must necessarily be some disavowed content, which isn't static but constantly changes as you change in relation to the person. The revelation of this content, its Real intrusion, forces the dissolution of that self. We can see this in the end of the film when Jude Law and Natalie Portman's character get back together. Many people react to this scene as being unbelievable, "how can someone change? fall out of love 'just like that!?'"
But that was the secret which the self-in-love-with Jude Law could not reveal, when he forced her to reveal it, that self vanished, leaving only an insistent ickiness about his behavior unfiltered with feelings of in love.
What the film forces us to miss, with its "cool" amibguous ending, which hints at some overarching, farreaching duplicity on behalf of Natalie Portman, who never was the one that Jude Law loved, is this crucial point. Relationships are not buily upon lies, but they are buily upon secrets. Secrets which because the truth of such is not a revelatory practice but a deconstructive lever, is not some object which can be illuminated by truth, but is instead obliterated by it. What the "she was never really the one he loved" thesis misses, is that we never are that person in love. If Lacan's too often quoted thesis "there is no such thing as a sexual relationship" is true, then what we see in every relationship is the creative, innovative attempts to overcome this prohibition, which requires the fromulation and reformulations of different versions of the self, different ways of cutting the self in order to reach the other that is loved. Each person possesses a kernel according to Zizek, and ethics and love are built around the relationship to that kernel, but what we can't ever forget is that our relationship to that kernel requires we recognize the multiple selves which are always already embedded and embedding, preventing us from ever directly encountering that, but always looking and loving awry it.
Moving on to truth. What is interesting in the film is that each character's positions in the film are guided by how they relate to and understand the functioning of truth. This is what sets apart Clive Owen as the film's Superman, in that he amongst the four knows best what truth and truth telling is. For the others, truth is a paralyzing, colonizing force. What sets Owen apart is the understanding two things. First that, honesty, the telling of truth, the forcing and revealing of it shouldn't be linked automatically to any morality. Good and honest are not necessarily the same, and this is because of the second thing he understands, in that the truth is almost always strategic. Telling of the truth always involves a manipulation, a strategy on behalf of the truth teller. When Owen forces Julia Roberts to admit to the dirty truth, when he reveals to Jude Law his sexual liason with Natalie Portman, what we see from these scenes is that truth and its telling doesn't give one any automatic position of morality and ethical uprightness.