I just discovered this photo browsing dA. What an amazing catch! I say catch because you took the photo at the exact right moment, and I mean the exact moment, timed in milliseconds.
Emotions are fleeting and I can't imaging that this man's facial expression lasted more than just a few milliseconds. Great timing and to stay away from cliches, I will simply say that your captured the moment perfectly.
Good photographs are ones that elicit an emotional response in your viewers and this one does that powerfully. It is obviously impossible to get in the man's mind but clearly, he's feeling some strong emotions, perhaps sadness or even devastation.
The obvious suggestive nature of the photo is that the emotional response was triggered by the other man in the photo, whose face cannot be seen: Brilliant!
Technically, the photo is spot-on. The square format works really well here focusing your viewers' attention on the men. The B&W works beautifully as well and one can only imagine the beautiful blue or green of the man's eyes.
Grain on the photo adds a bit of nostalgia and the relative shallow depth of field gives beautiful depth.