I don't, and there are several reasons:
1: My wife. I don't want to cause her the distress and grief. I love her. Despite my efforts to absolutely release all irrational thoughts, my feelings toward my wife are something I'll never let go.
2: Fear of death. Also irrational, but the abyss is a terrifying concept to my human mind. What lies beyond? Well, it might well be nothing. But I've never been dead. And even the idea of an end to my self is terribly scary; I've never ceased to exist before.
3: Hope for something. I don't currently accept any inherent meaning in life and existence, but I sure wish there was some kind of purpose. Another irrational desire.
There is a good reason it took so long for me to admit my serious doubts about my religion; I desperately, irrationally need meaning. I assume others experience similar feelings, and I assume this is where the sentiments arise that "life is not meaningless just because there is no universally-defined purpose to it" among atheist commentators and authors.
Of course, suicide is as irrational as any course of action. There is no real reason to decide to do anything.
I think the suicidal ideation, however, is a coping mechanism when I feel particularly uncomfortable. I know I will never go through with it, however much I toy with the idea and dream up methods; I just want to imagine a fool-proof escape from everything I feel pressured to do and be.
I recognize that everything I do is irrational and does not fit with my view of the world. In fact, to everyone but one or two people, I appear to be a devout Christian, faithful husband, A-student, Eagle Scout on the fast track to eventually receive a PhD in Physics. And in fact, I guess I am those things in all of my actions, but I don't think like the idealized person I pretend to be.
I practice religion for appearances, out of habit, and to support my wife. I do well in school and have chosen a challenging and intellectual career-path because that is how I was brought up.
I will always be faithful to my wife. She is my strongest true tie to the world of the human experience and the preoccupation with all things human. She makes me feel and hope.
I guess what I regard as my considerable intellect is conquered by my love for my wife.
I hope beyond all rational conclusion that my current take on existence is a temporary step that will eventually lead to some kind of feeling of meaning, purpose, and peace.
I won't pretend that I'm not miserable, but I don't know what to do about it. My reaction is simply that of a human being unprepared to accept a harsh, meaningless reality.