Nico hates Percy. That's just common sense throughout the camp. Nico is like a hermit. He doesn't talk much. He doesn't do much. When Will Solace hit on him, Nico turned him down in front the entire camp. He doesn't do people. But he hates Percy. That's what they think, at least. In all reality, the two demigods are in love with each other. They just won't get over themselves and admit it.