This one broke my heart
http://www.mangago.me/read-manga/kyuuso_ha_cheese_no_yume_omiru/ (sequel: http://www.mangago.me/read-manga/sojou_no_koi_wa_nido_haneru/)
It really did! Its soo damn realistic I nearly cried coz of frustration.
Right! ╥﹏╥ The first time I read it, I cried for real because it felt like the manga was based on true story.
Well, I guess Rules series would fit pretty well. It always causes me great pain.
http://www.mangago.me/read-manga/croquis/ ch. 5 & 7
http://www.mangago.me/read-manga/touch_me_again/
http://www.mangago.me/read-manga/illumination/
http://www.mangago.me/read-manga/dog_style/
http://www.mangago.me/read-manga/senya_ichiya_shitone_no_himegoto/
http://www.mangago.me/read-manga/gravity_eyes/ more like bittersweet
http://www.mangago.me/read-manga/okubyou_na_yubisaki/
http://www.mangago.me/read-manga/uminari/
http://www.mangago.me/read-manga/kimi_no_kao_ni_sasu_kage/
http://www.mangago.me/read-manga/koi_no_katachi/
http://www.mangago.me/read-manga/subarashii_shitsuren/
http://www.mangago.me/read-manga/yagate_ao_ni_naru/
http://www.mangago.me/read-manga/mimurake_no_musuko/
http://www.mangago.me/read-manga/natsujikan/
They made ME sad, I can't guarantee it'd be the same for you.
Thank you I'm going to read everything
I want to read so sad yaois~ I wouldn't mind if the unrequited love becomes requited or not. Also preferably yaoi not shoujo ai