Nevermind, I reread your post. My recommendation is not bl. It will still leave you in tears, but not bl.
Does it have to be a manga/ webtoon, or do you also read novels?
http://www.mangago.zone/read-manga/10_years_where_i_loved_you_the_most/
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http://www.mangago.zone/read-manga/i_will_be_waiting_for_you_in_1999/
this one was a different type of hurt, idek man. it wasnt even THAT sad but gosh i cried like a bitch xD
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http://www.mangago.zone/read-manga/mahoroba_no_hibi/
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http://www.mangago.zone/read-manga/lonely_to_organdy/
this one also hurt like hell
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well you did ask for sad bl recs so im hoping they are to your taste. maybe im just emotional but i cried reading all of these. enjoy! (づ￣ ³￣)づ
Have fun (๑•ㅂ•)و✧
http://www.mangago.zone/read-manga/banana_fish/
if anyone can recommend some bl that will have me crying my guts out that would be great