some*
for example like this manga :3 it doesn't have to be just like this one tho
http://www.mangago.zone/read-manga/kyou_mo_ashita_mo_asatte_mo/
2nd story of http://www.mangago.zone/read-manga/toriaezu_kiss_shite_kudasai/
(Chapter 4) Hope u like it!
Unrequited love + sad + happy ending
http://www.mangago.zone/read-manga/lover_boy_lezhin/?av=3
http://www.mangago.zone/read-manga/kimi_ni_ageru/
http://www.mangago.zone/read-manga/cosmic_boy/
http://www.mangago.zone/read-manga/sayonara_heron/
http://www.mangago.zone/read-manga/dare_mo_ga_aisaretagari_no/
http://www.mangago.zone/read-manga/hyperventilation/
Start with this one
http://www.mangago.zone/read-manga/intense_lee_kyung_ha/
For more
http://www.mangago.zone/home/mangalist/622485/
http://www.mangago.zone/home/mangalist/622486/
http://www.mangago.zone/home/mangalist/622487/
What are so good yaoi manga that has unrequited love in it and its kinda sad but in the end they both end up liking each other and its happy :p