Personally I think it's about a guy who has fallen in love and while he was happily in love he thought everything was possible, but then the girl broke his heart and his world crumbled. Now he blames himself because he was "too slow."
I think "Watch me reap the pain that I have sown" means that before the girl broke his heart he invested a great deal of time/affection on her and now it's turned against him, turning into the pain "he has sown" -- this also makes sense because he is blaming himself for this failure.
"Every smiling face brings him down" because they remind him of her or of happy moments with her prolly.
Personally I think it's about a guy who has fallen in love and while he was happily in love he thought everything was possible, but then the girl broke his heart and his world crumbled. Now he blames himself because he was "too slow." I think "Watch me reap the pain that I have sown" means that before the girl broke his heart he invested a great deal of time/affection on her and now it's turned against him, turning into the pain "he has sown" -- this also makes sense because he is blaming himself for this failure. "Every smiling face brings him down" because they remind him of her or of happy moments with her prolly.
Dunno, that's just the way I see it.