Are you sure it's not sweat? And if he is really crying then I think it's the song lyrics getting to him. I look at most of kpop group songs, as a journal in a way.
They only write/record/sing on things that have happened to him. I'm guessing he is kicking himself for letting some girl go and not try and keep or fight hard enough for her. Something along those lines.
I have to agree with you. He is extremely handsome! I could get lost in his eyes.