After Nico had given up his position as the ambassador of Pluto to go back to Camp Half-Blood after the Greek and Roman camp war. When that war ended, the quests being over, and Jason's pleading words, Nico had decided to give Camp Half-Blood a second chance.
But there was another reason why he wanted to stay at Camp Half-Blood. You were that reason.
You first joined Camp Half-Blood just a few days after the second war had ended, being brought in by a satyr in a frenzy, for you were a rather powerful demigod, at least with your aura that attracted one too many monsters during the first few days at camp.
Nico, as always, observed by the shadows, keeping his eyes on the new fellow camper who's been causing quite a commotion for a newcomer. And that observation slowly turned into- Nico thought to himself with a shudder- a crush.
Nico knew that he shouldn't just randomly fall for someone. But when you first introduced yourself to him, holding a hand out and a grand handsome smile... Nico didn't even know what to do. So he stayed at Camp Half-Blood, willingly for his friends and this new person.
You were not off-putted by Nico, unlike many campers. He was the residential 'loner', given that he was the one and only son of Hades. But you didn't let that stop you from trying to befriend the teenage boy, charming your way. And after some time, you may have also developed something for him. Whether it was out of respect or genuine romance, you wanted to make sure that you didn't show off too much-unwanted attention towards Nico.
One day, during their daily hangouts, it was time for Nico to finally confess. You were getting ready to start a fire since both of you wanted to hang out in the woods without anyone else around. This was the perfect opportunity for Nico, as he slowly fidgeted with his hands as he spoke.
"So... there's something I've been meaning to tell you." Nico started, his brown eyes staring down at his trembling hands. He could feel his heart race. "It's just that... Well... I like you."