These two popped into my head after reading the word "heartbreaking"
This one is sort of a shounen ai but its sad, (i liked Hiromi's story but you should Read Haru's story!!), its the best one, its starts off with his parents' story and with him being born but keep reading it cuz later it shows him in high school then grown up, and the heartbreak continues T-T http://www.mangago.me/read-manga/is_otoko_demo_onna_demo_nai_sei/
This one as well, I could not stop crying with this one too, i just,... idk just read it T-T
http://www.mangago.me/read-manga/bokutachi_futari_ga_koisuru_riyuu
Hana to Ryuu
Do anyone have sad/heartbreaking/touching yaoi mangas ? Shounen ai also can ^^