http://www.mangago.zone/read-manga/kuroneko_kareshi_no_itoshikata/ Tho he don’t have blond hair (meh)
Okeyokey, I have one thing to say first: A yaoi with a blackhaired uke and a blond seme is literally 90% of all the yaois out there lol. But I went through the yaois I’ve read so far and found this for you, and it’s with either the main couple or the side couple there that matches your describtion. I hope you’ll be able to find it!
Yaoi: Blond seme and blackhaired uke
http://www.mangago.zone/read-manga/ijiwaru_shinai_de_dakishimete/
http://www.mangago.zone/read-manga/walk_on_water/
http://www.mangago.zone/read-manga/hyperventilation/
http://www.mangago.zone/read-manga/furete_aishite_dakishimete/
http://www.mangago.zone/read-manga/the_baker_on_the_first_floor/
http://www.mangago.zone/read-manga/sayonara_game_minaduki_yuu/
http://www.mangago.zone/read-manga/love_nest_minaduki_yuu/
http://www.mangago.zone/read-manga/wolf_in_the_house/?hcgo
http://www.mangago.zone/read-manga/from_points_of_three/?3HmV
http://www.mangago.zone/read-manga/jikyuu_jisoku_de_nani_ga_warui/
http://www.mangago.zone/read-manga/bokura_no_negai/
http://www.mangago.zone/read-manga/mad_cinderella/
http://www.mangago.zone/read-manga/if_you_hate_me_that_much/?qMNb
http://www.mangago.zone/read-manga/brothers_yamamoto_kotetsuko/
http://www.mangago.zone/read-manga/mankai_darling/
http://www.mangago.zone/read-manga/kizudarake_no_hakoniwa/
http://www.mangago.zone/read-manga/lover_boy_lezhin/?kIJk
http://www.mangago.zone/read-manga/see_you_agai/
http://www.mangago.zone/read-manga/royal_servant/
looking for a yaoi where the uke is a black Neko and the same has blond hair