'Ware the warnings. They're there for a reason.
He was so young still: a child, a helpless child. Older than when he had betrayed Narnia, but still so young, so young. Without the comfort of Aslan, of Narnia itself, was it any surprise that Edmund was struggling? No one could be perfectly vigilant at all times, especially when, well, the others were struggling too, and had their own grief to contend with.
But he was the only one who stole a knife from the kitchen.
It started gentle, at first, scars so small they were only visible if he looked in good lighting. It did not stay gentle: not that gentle had ever been the word to describe it.
One night he was sitting, mute with agony, in the bathroom that seemed the only place he could count on privacy. Memories, beautiful Narnian things all twisted and broken up by absence, crowded in his mind. He remembered his betrayal, remembered the Witch, and the terrible cold. For a moment it seemed the cold was curling around him and possessing him, and a sudden horrible feeling overtook him, for he wanted it to, and in an instant, was convinced he deserved anything and everything he could do to himself.
He felt he should be weeping, tears should be spilling from his dry, unfeeling eyes, but he was numb, except that his knuckles grew white about the stolen knife. There was no pain, not in that moment: not even a whisper of it, but looking at his handiwork he curled into a small ball (so small, so young, such a child) and put his face on his knees and said instinctively, "Lucy! Oh, Lu..." and wished brokenly for her cordial, and that somehow it would heal his soul, too. "Aslan help us all."
And the door opened. Lucy did not scream, did not even cry out as he might have expected. But he looked up and saw her gaze.
"Oh, Ed," she said, in a whisper, and came in quickly. "Why?"
He shrugged up tighter, and said, in a muffled voice, "Dunno." After a pause, during which Lucy came closer and shut the door, he added, "I deserve it."
"Aslan's blood was spilt because of your mistake with the Witch, yours need not be!" she said, voice rising, then looked guilty because of the noise, and whispered, "Sorry."
"But I do deserve it," said Edmund in a muted tone. "All my mistakes, and problems, and all the things I've done wrong. I can't deal with them otherwise, Lucy. And all the memories! I have almost no specific memories from Narnia, but enough to know that I miss it, so badly. And I'm not enough, not strong enough like you."
"Why!" she said, voice soft with surprise. "It's not me that's strong. It's Aslan."
I'd already started this chapter, but I finished it off very much because it's a distraction, to write about it rather than to do it. And on that note: don't harm, kids. Please don't. It's not worth it to start, no matter what the reason you have. I promise there are other and healthier ways to deal with it. Whatever your mind tells you about your worth, and if it tells you that you deserve to harm yourself, that's a lie. Your mind is playing tricks on you. Take courage, and please take care of yourself. God knows it isn't easy! But I beg you, don't go down this path. Once you've gone down it it's so much harder to come back out of it: and that I have not managed, though I know those who have. In the moment it might seem the right thing to do, but it's not, it's not, and if there's anything I can do to help anyone, anything in my power, I will, God willing. But cutting is an addiction like any other, and takes great strength to get out of. God go with you.