Some people believe in love at first sight.
And sure, it might exist. It could be possible. But not for Nico di Angelo. Love crept up on him, slowly forming roots inside his heart until it was there to stay. Even he wasn't aware of it for years, until the incident with that blasted Cupid. The god of love turned his world upside down, and Nico knew it.
It started simply as admiration. Nico felt about his love as a role model, then a friend to turn to in times of need, then a big brother. It was only when Nico summoned that undead army that he realized that, no matter what, he couldn't hurt the Son of the Sea God. He cared too much about him.
Jason talked to him about it many times, reassured him over and over that nobody would judge him for who he was. But Nico didn't believe him. Besides, he only cared about the opinion of one person. And he and that person didn't play for the same team, he was sure of it. Not when Nico's love interest was gazing at Annabeth as she teased him and called him 'Seaweed Brain'. He hated them and he hated himself, but that didn't stop the Ghost King from feeling the way he did. He wished so desperately that he could tell his loved one how he felt, but no. It wasn't possible.
After all, how could the boy who had gone on so many quests, saved Camp Half-Blood and Olympus, become a praetor, and so much more show any interest in Nico whatsoever? The son of Hades was permanently stuck in the friendzone, and he knew it.
But Nico di Angelo would always love Percy Jackson, just the same.