Apollo
He is bright. Brighter than any man you could possibly ever meet. He is charming and bearing, but when too hot and burn you until you just can't take it. He's emotional and loving, though would never let any see it. He is possessive and protective, having almost every person, lover or not, get taken away from you does that to a person (Nico could easily relate to that). He can be over dramatic and selfish, but in reality, its just one of his types of ways to not showing his emotions. Not showing that losing almost every lover he has ever had still hurts him.
How it hurt when Daphne thought she could be happier a tree then his wife. How it hurt when Hyacinthus died in his arms, or how Cassandra only used him for his money and looks. How Coronis had bed another man with his child, and Cyparissus who lost his life and turned into yet another plant. And that isn't even half of them. But with this boy, this beloved shell of a boy Apollo had some how fell for worked way into his heart, and probably didn't even realise it. He was afraid he would lose his precious Ghost King and that he would turn loveless.
Because when he shines too bright, Apollo can always count on Nico and his shadows too darken it up a bit.
Nico
He was a loner. You would never catch him with anybody other than his sister and even she was rarely around. People didn't understand him, think in his way, so he had just decided tune them. People will only hurt you in the end right? That was the excuse he would always make. Then one morning he finds haikus in his front porch at camp and it all begins. First he finds out who this mystery person was, next thing you know you're hanging out together and suddenly being made love to in the back of a certain sun god's car (it's actually a chariot, but thats only to impress the people). He doesn't know how it happened or if he wants it to stop, but it was definitely not a fling. . .At least, not to him.
Because when the dark becomes too much, Nico Di Angelo can always count on Apollo to light up his world.