Plz recco straight colored romance about mafia or gang

http://www.mangago.zone/read-manga/gokusen/

http://www.mangago.zone/read-manga/raise_wa_tanin_ga_ii/ Not exactly a gang leader but he’s in the yakuza and she is too

Midnight Poppy Land, it's on WebToon though

http://www.mangago.zone/read-manga/black_dragon_s_lover/
http://www.mangago.zone/read-manga/jiji_koi_70_sai_yakuza_wakagaette_koi_ni_tekozuru/
http://www.mangago.zone/read-manga/sun_ken_rock/
http://www.mangago.zone/read-manga/queen_1/

this one is shounen ai but you might like it:
http://www.mangago.zone/read-manga/excuse_me_dentist_it_s_touching_me/