is there a story with bl harem? does it exist or nah?

they exist alright, use the genre filters and you'll find alot

omg wait like nothing comes up, here;
http://www.mangago.zone/read-manga/manager_ni_natte_mo_mondainai/

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

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

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

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

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

most of these are more threesome's than harems though-

yeeeess :<<< thank you tho (づ￣ ³￣)づ