I Think About Suicide

I'm obsessed with blood. Sometimes I really really want to cut myself so that I can see it come out.
I also feel like I'm being crushed--drowning at the bottom of the ocean where there isn't any light and crushed by all the pressure like a tin can.
All I can think about it that I want to die. I really don't, but I can't think about anything else. Lately I also hear people that aren't there telling me you deserve to die for having these disgusting thoughts, you're a failure (my grades are dropping), you're stupid, etc. Once this started, I've had a lot of trouble concentrating on anything due to all the confusion, and everything takes longer because I lose my line of thought.
I used to write poetry, which helped (or maybe not...hmm). When I couldn't write anymore, I tried drawing, which didn't last long. I run long distance--I had stopped about a month ago when I stopped writing, but today I started again. The running definitely helped my stop thinking altogether, and I think I prefer the physical pain over what I think is depression. Not that it ever goes away, but it seemed to get better when I was running.
In a way, I've started writing again today (because this is writing). I was in a similar situation a couple years ago (but not nearly as bad--I told my parents, and they told me suicide is selfish. At the time I felt antagonized, but now I realize they were right. Mostly I think this is my fault and I shouldn't think about killing myself but I can't help it and I just want the thoughts and voices to go away.
I just wanted to get this off my chest so to speak and offer the tip about running, because so far it seems to have helped. I think the best way would be to go in the water and cut my wrists. That way even if I don't bleed to death I'll fall in the water and drown, they'll never find the body.
But I'm getting better, I think.