haruki's gimmick is that he tries to play the tough guy act and tries to deny his "feelings" . But you can only act for so long before you break character and show the "true you". It has been shown before through both Haruki's and Shoichi's route that Haruki respects and admires Shoichi, he just doesn't want to show his emotions to the people around him because he thinks that makes him a " mushy person" or masks those feelings through insults. The news probably were so shocking to him that he broke character.