The Penny Dropped
Breaking Point by SMANGST
Sam blames himself for everything and sees only one way to escape.
It ends when you can't take it anymore
Choices by MinionMooskateerAckleholic
Sam can't take much more. Dean and Bobby are stretched thin...but Lucifer never gives up.
Hallucination Fix by InvincibleIsabelle
In which Sam kills himself because he can't stand the hallucinations after his wall broke.
None of the Above
It's Not Suicide If We're Already Dead by x_luciole
"What are you saying exactly, Sam?"
"That I want to make it our time." Sam pulled his gun.
Sleepy Vitamins by Onceuponademonhunter (also here)
No one could save him now. Sam was too far gone for saving.
When It All Just Gets Too Much by Me And The Time Vortex
What happens when Sam gets low? He doesn't know what to do anymore.