If someone had told him he was destined to be alone forever, Leo would have believed it. It felt like it was part of his destiny, one he would not want to embrace.
It all had its origins when Gea forced him to kill his mother, something he felt too guilty to admit, so much so that he always lied about her death. Things were not for the better in any of his foster homes. Most were abusive, too much so-called.
Things came to a head when the 7 of them got together to save the world from the goddess Earthface. Leo had felt so useless, as if his only function was to fix the Argo II (even though he was sure Annabeth could learn to do it, and then he would be 100% useless) and he also felt left out. It could have been because everyone on that ship had a loved one, or because he had certain strained relationships with several of those present.
Once the war was over, everyone returned to their respective camps, with the exception of Jason, who stayed at Camp Half Blood instead of returning to Camp Jupiter.
A part of Leo was saddened by this. Don't misunderstand; Leo was very fond of Jason, after all, they were supposed to be best friends. But he and Piper were a couple, and whenever they were together (that is 90% of the time), they stayed together in a romantic way, and ignored the Latino.
Sure, he could have talked to Percy and Annabeth, but they were preparing to attend college in New Rome, and he would only be a hindrance to them. And Frank and Hazel were off the list altogether; for the love of the gods, his great-grandfather and Hazel had been dating before she died. He knew how awkward it would be for all three of them.
He could also have tried to relate to his siblings, but he didn't feel able to. All the relatives (and people in general) with whom he had had close contact ended up hating him, loathing him or dying, and he did not want that fate to repeat itself again.
All, all of that led him to be where he was now; sitting in bunker 9, with a handmade knife in his trembling hands.
He pulls down his shirt sleeves and the show begins; first, he cuts his wrists, perhaps his favorite part to cut. The pain feels so pleasurable, and makes him feel alive inside as it punishes him while relieving his sorrows. The blood reminds him that he is still alive, in a painful but relieving way.
Go on, Says something inside him.
Leo moves on to the next part of his body to be cut; his thighs. He runs the knife gently across the right thigh, hard enough to bleed without making any large wounds (although it is obvious that there will be scars, as always, but that is the price to pay), but still feel the pain he craves. He goes on like this for a while, taking turns between wrists and thighs, trying to make it bleed without bleeding out.
He knows that he has to choose areas that are not very visible or harmful. Thighs are perfect for this, but wrists are dangerous. Still, he doesn't think much of it, because the idea of being on the brink of death thrills him a little. What is life worth living for, after all?
He just doesn't do it because he knows it would devastate his younger siblings, and he's not willing to let anyone else suffer because of him. They don't deserve to know death at such a young age.
The hours pass, and Leo notices that it's time for dinner. But he's not hungry, much less eager to go out. He knows that his dark circles under his eyes will highlight his lack of sleep for 72 hours, 72 hours in which he had worked non-stop in bunker 9 just to distract himself. People (the few who really care about him) would start asking questions. And he's not in the mood for that. He has to do it, though. If he doesn't go, he'll just draw more attention to himself. Maybe he actually does want that, but not for those reasons.
Instead, he nibbles on a piece of ambrosia that reminds him of how good his mother's tacos tasted, and gets in the shower. He wipes the now-dried blood from his thighs and wrists.
Once outside, he puts on his favorite pants and his favorite long-sleeved shirt with suspenders, before leaving bunker 9 and heading towards the pavilion.
