Okay, "The Departed" and the Whole Doppelganger Thing?

So, I finally got around to watching "The Departed." Yeah, I know, way late to the party! But with the kids finally old enough to appreciate a good crime movie (and not completely freak out), we gave it a shot. It's definitely intense! What struck me, though, was the whole mirror image thing going on between Colin (Matt Damon) and Billy (Leo DiCaprio). They're both living these fake lives, playing roles, and it's like their worlds are constantly reflecting each other, distorted and dark. My theory is that the film is basically a Greek tragedy dressed up as a gangster movie. The whole destiny thing seems pretty strong, right? I mean, from the moment Costello (Nicholson, who is terrifyingly good) picks Colin, it feels like he's setting him on this path that he can't escape. And Billy, volunteering as a way out? Both of them want different lives but are trapped by circumstance and the choices of others. The constant use of mirrors, reflections... even their romantic relationship is mirrored - they're both involved with the same woman! It kinda hit me during a particularly intense scene (no spoilers!), that neither of them were ever going to be truly free. Like, even if they "won," they'd still be haunted by what they'd done and seen. It's heavy stuff, especially when you think about the sacrifices they both make, or are forced to make. Anyway, just my two cents! Curious to hear what others think about all the duality and "destiny" stuff. Am I reading too much into it or is it totally there?