For me it comes down to two thoughts. (And I ruminate about these near constantly, and talk myself out of doing myself in multiple times a day.)

Yeah. Rumination. What I always come back around to is that whatever happens I don't want to increase the total amount of suffering in the world if I can possibly help it. The way I see it, if I had to spend the next 20 or 30 years curled up in the fetal position stoned out of my mind, the total amount of suffering I could experience couldn't possibly approach the suffering that others would feel if I were to take my own life.

That said, I still fight the impulse every day.