the funeral ;P
This song isn't really sad, just brings back memories (kingdom hearts 3 fuck yes)... it's pretty damn sad though.
Marylin Manson - Spade
I think for me it would easily be Johnny Cash - Hurt. You can hear the death in his voice when he sings this song. Sad knowing he is now no longer around and an artist I still listen to till this day.
SOD - Such a lonely day
XXXTENTACION - Save Me (Ft. Yaprak Asimov)
It's not the saddest but the way X screams "Fuck, fuck, fuck, we doin' " in the end of his part makes me a little bit sad, it makes me want to kill someone or to set everything on fire and then kill myself (I'm weird xdxdxd)
"Only Love Can Break Your Heart by Neil Young" is the saddest song ever heard.