check out those that have a "tragic end" mark
http://www.mangago.zone/home/mangalist/72632/ those are the ones that have their lover died.
http://www.mangago.zone/read-manga/the_inheritance_of_aroma/ - The ending's beautifully killing me, I really love this one.
http://www.mangago.zone/read-manga/hybrid_child/ - You may have already read.
http://www.mangago.zone/read-manga/kin_gin_kokoro/ - For me, the ending killed this manga.
http://www.mangago.zone/read-manga/10_years_where_i_loved_you_the_most/uu/10_years_where_i_loved_you_the_most-chapter-1
this one is really painful. Happy tears ( ̄∇ ̄")
Searching for yaoi where the uke dies at the end and Seme in lots of pain/suffering.