You're on a wrong logic path. You say that self harm leads to suicide, because you've heard about people who used to self-harm at first, and commit suicide then. But I'll tell you that the reason of the suicide is not a self-harm, it's pain and depression. You consider suicide as the last option to end your pain. And, if self-harm reliefs the pain, therefore it makes you live longer, as long as there's another option to end your pain, despite it's a temporary solution.

Believe me, no one truly wants to die. I want to die in my overwhelming painful depressive episodes, and I tried 3 times to do this. But I don't want to end my life, no. I want to live a happy, painless life. But there's so much pain, that I forget about all the good things I experience in my normal days, and these times, the intention to end the pain fights with the fear of death, or fear of worse pain while being in agony of dying.

I know that someday fear of death will loose this battle, and I'll do this. But I'm still alive, and, partially, thankfully to self-harm.