Elliot Smith was amazing, and his stuff was pretty dark, but here is my vote. Not a rock song, but by an artist called Immortal Technique. It's called "You Never Know", this is the last little bit.
"Nobody loves you more than me carino" is what the letter said
but by the time you get to read this, I'll probably be dead
when you left in '97
a part of me went to Heaven
I thank God at least I got to know what love really was
But it hurt me, to see what true love really does
'Cause even though we never made love, you were all that there was
It was because I loved you so much that I had to make you leave
You made me doubt the way I thought, you made me want to believe
And then I slipped up, and I let you get close to me
It was hard to not be openly when people spoke to me
This was not the way I thought my life was supposed to be
Baby don't you see, I had a blood transfusion that left me with HIV
Hoped the end exists for me since late in 1993
I died a virgin, I wish I could've given myself to you
I cried in the hospital because there was no one else but you
Promise that you'll meet me in paradise inevitably
No matter what, I'll keep your love forever with me"
What happened for the rest of the day is still a blur
But I remember wishing that I was dead, instead of her
She was buried on August 3rd
The story ends without a sequel
And now you know why Technique, don't f***ing fall in love with people
Hold the person that you love closely if they're next to you
The one you love, not the person that'll simply have sex with you
Appreciate them to the fullest extent, and then beyond
'Cause you never really know what you got, until it's gone