well, I jusst cut up my arm and my stomach. so much for positive thinking. I just can't take this shit sometimes. I feel like a failure but I'm not dead and if I did what I wanted to I would have taken all my meds and a bottle of red wine then I'd be free of all this but I'm hangin on for some reason. 
For the past thirty years I've experienced irregulaly spaced depressive episodes that made me want to throw myself down a well, but I got through with the help of friends and the knowledge that things would eventually improve.
I hope you aren't keeping all this to yourself, because that only makes it worse...if you don't have a therapist, at least talk to friends or someone at a crisis hotline. When I finally started, talking to people was one of the best things I did to make life more bearable.
Good luck, we're pulling for you.
Life isn't always easy, it's hard and the fact that you feel like total shit and have made it this far proves that you are a strong, good person. And a person as strong and good as you is definitly worth keeping around.
About the cutting, when I first read it, I just wanted to scream..."NOO" But I understand. I don't know what to say to you about that because no matter what people tell me, I used to do it anyway.
Please don't keep any of this to yourself. Talk to other people than just typing it on here. While typing here may get rid of some of it, you need to talk to a real person. Call at hotline like Boo_Radley suggested, talk to friends.
If you need someone to vent to, I am here, well internet wise anyway.
Please realize that life is worth living, and if you decide it isn't, just remember that if you did kill yourself, you will regret it. Whatever you believe in, or if you believe in nothing at all, killing yourself will only bring you a step down from what you are already experiencing.
Take care