Kamis friend realized Kami's feelings, and he felt quite bad about it in a sense that 'how could i do this to him.' since he made him his best man. That's why he wishes happiness for Kami, because even though he doesn't feel the same, he as a friend failed to really make him happy.
In the sequel Kami gets his happy ending, and we also get to know his friends say on it all. (●'◡'●)ノ
http://www.mangago.me/read-manga/renchin/

Wait... In chap 5 "THE FIRST BITE".. Did the guy realise that Kami loves him or did he realise that he also liked him that was why he was crying??