Alone in mind, not in presence,
The boy cannot do this.
He has gone on for as long as he could, but the knife isn't enough anymore. No amount of physical pain can distract him from his bleeding heart and howling soul.
He types an email instead of writing it, because his hands shake too hard.
He writes a different one for each person and hits send. Nobody will know until it's too late: the clock reads 3:16 AM, and he's hundreds of miles away. He does handwrite one thing, however: he leaves it on the counter in an envelope, the front of which reads "Mom".

He exits his bedroom, and takes a last look at his surroundings, kisses his sleeping 6 year old sister on the head one last time, and walks to the balcony.
He remembers, two years ago, when she fell.
Fitting, yet ironic, he thinks. that he would leave the same way. He looks at the stars, whispers "Goodbye," and leaps. The cool night air rushes around him momentarily, then-nothing.
.
..
"Hello?" he calls into the nothingness. No answer.
He calls again, with the same result.
Slowly, the painful reality of his situation dawns on him, with horrifying clarity:
This is the afterlife, and it is worse than the real world was.
But it's too late. He can't take it back, and he is doomed to eternal  loneliness and complete nothingness.
*Forever.