Responses
Dunno if they're sad enough:
http://www.mangago.zone/read-manga/omerta_kochou_no_yume_no_kate/
http://www.mangago.zone/read-manga/bi_no_isu/
http://www.mangago.zone/read-manga/aiso_tsukashi/
http://www.mangago.zone/read-manga/blind_love/
I bet you know this one, but I have to mention "Totally Captivated" as well (it's not Yakuza, but Korean mafia).
Hiiiiiii minna san,,please recommend me yaoi with sexy and hot seme yakuza, sad story with happy ending thank you ヾ(☆▽☆)ヾ(❀╹◡╹)ﾉ~