Nico didn't know what to do, how to get out his feelings. Will died, and so did Hazel. 
She knew Will would keep Nico from committing suicide if she died, but she wasn't sure what he would do if it was the other way around. She was sure that Nico would pretend to be happy, but Will had a knack for getting the younger boy to let it out. 
But Will died. He had screamed "You can hurt me, you can torture me, but for the love of the gods, don't touch _him_!" and charged into battle. Those would be his last words, apart from his battle cries. 
The last thing Will Solace saw was Nico's worried face as he bent over the blond's barely breathing body. 
Nico had nobody. Percy and Annabeth were gone; no one knew where they went. Frank was being comforted by Jason every day. But Nico? No way. He wasn't going to Jason; he did that when he had a crush on Will, fangirling with him. Piper was helping Jason with Frank, she didn't have time to go to a low-life son of Hades like himself. 
Leo and Calypso? They just moved in together; they had a baby to take care of and everything. He didn't want to pester them with their problems. 
But then something happened.
Just as he was about to express how he felt through a thin piece of metal, Percy showed up, carrying band-aids, anti-bacterial cream, a blanket, and set to work, throwing the razor away, Nico didn't know what to say. 
When Percy was done spreading the cream over any-where Nico had expressed what he felt and putting a bandage on it, he wrapped Nico up in the blanket. 
It was soft, and warm. It smelled like Will. 
"Why did you do that?" Percy asked, gathering the now-crying son of Hades in his arms. "What about Will, and Hazel?" Nico cried harder. 
Percy understood and picked up Nico, carrying him over to his bead. He tucked the younger boy in and curled up next to him, whispering "You're gonna be okay, Neeks. I promise."