RpNation

Any relatively good "dark" song is also fine, it doesn't solely have to be about death or suicide. 

Hotel California is all about Addiction


Under Pressure is about how stresses from life can destroy us

as an emo kid, depressing songs about death are kind of my specialty...


Cemetery Drive by My Chemical Romance


is definitely about suicide, Helena would also work quite well, as could Dead!, or even Welcome to the Black Parade.


Wonderless by Pierce the Veil isn't directly about suicide, but it could easily be interpreted that way. Bulletproof Love (also PTV) is about suicide, though for a specific reason that might not fit what you're going for. Yeah Boy and Doll Face, as well as Stay Away From My Friends by them reference self-harm and possibly an attempt.


Second Guessing by Get Scared is a good one about being suicidal, The Devil's In The Details also fits that mindset. 


Hello Darkness by New Year's Day might be perfect for you, actually... definitely give that one a try.


Tourniquet, Swimming Home and My Last Breath by Evanescence would all work as well, if you're looking for something more with a more haunting feel.


i'm sure there's more, these are just a few off the top of my head... good luck on your project!

Kavinsky - Nightcall (if you are looking for something with a dark 80's ambiance)


Frou Frou - The Dumbing Down Of Love (i guess this is more of a "sad" song, but it could be good for a depression topic)


The Police - Can't Stand Losing You (about a guy willing to kill himself over a break up)


The Police - King of Pain (another dark song I suppose?)


I hope these help! I might be able to find you more.