Sometimes he wants to thank him.
He can't even really begin to fathom how inappropriate this would be. For a lot of reasons, really, the first being that it seems like an asshole move, thanking someone for becoming a god and essentially leaving your life forever. Because they hardly see him anymore, because he's busy, doing, well, god things, he supposes. Like fighting wars at the bottom of the sea and talking to fish and finding Nemo, and such. Things which are not important enough for mortals like Nico to worry about.
Also, he can't even imagine how that conversation would go; 'I just wanted to thank you for choosing immortality and leaving us all to our pitiful lives on Earth so I can fuck your girlfriend.' Nico hasn't had a lot of experience in etiquette- he spent fifty years of his life chasing ghosts and shooting bad guys and deer, for the most part- but he's pretty sure that's not really something you thank somebody for.
Besides, he surely knows. When he's not out in the sea frolicking with his father (he seems to have forgotten the whole, abandoned as a baby thing) he has to be aware of the fact that Nico and Annabeth are on the land, frolicking in a way of their own. It's probably the reason he never visits anymore- but who knows. Maybe Ursula is getting out of hand, and he has to sort it out. Nico doesn't know what goes on at the bottom of the sea. Why would he?
But he really, really does want to thank him sometimes. Like when she's sprawled across his bed, golden curls spread out and beautifully, gloriously naked, and when she tilts her head and smiles tiredly and he gets to sweep a hand across her battle scarred back. Or when he gets to feel the rise and fall of her breasts or her deft hand which can do more magic than Harry Potter ever freaking could. Like when her legs are around his waist and her hands are in his hair and both of them forget they ever loved anyone else. He wants to thank him because Annabeth Chase really is the best thing to happen to him and it never would have happened if he was still alive (that's how Nico has been thinking of him- dead and alive. He knows this isn't technically true but it's almost easier to accept).
Annabeth stretches out next to him and then breathes on his neck, snoring lightly, naked and sweaty and just generally amazing, and he wonders if it would be totally, totally inappropriate to give him an offering at dinner tomorrow.
*
Sometimes he wants to kill him.
He knows you can't kill a god, but he could sure as hell hurt him, couldn't he? Because at certain times watching him spill golden blood (ichor, Annabeth would correct him patiently) would just be simply fan-fucking-tastic. Because how could he think this would be enough? Sure, Annabeth naked on his bed isn't something to bat your eyes at but that isn't always enough. Because he would never scoff at the things Annabeth scoffs at, and he wouldn't frown on staying out late and getting so drunk you couldn't walk straight, and he never gave a flying fuck whether or not Nico dressed like a fifteen-year-old emo girl. Because there are some moments in life when having a really hot girlfriend just doesn't cut it, and when Annabeth stands in the doorway and refuses to go anywhere near him unless he cuts his hair, well, that is one of those times.
He needs a best friend. And Nico doesn't give a shit if he's finding the Titanic or exploring the lost fucking city of Atlantis, because dammit, Nico needs him.
It isn't just Nico, either. Grover is only half the goat he used to be and even the rest of the campers who knew him don't seem half as lively during summers at camp as they used to be. Then of course there's Annabeth, who sometimes gets a far off look in her eyes and won't touch him and there's him, alone and mortal and best friend-less.
Annabeth rolls away from him and he wonders if it would be totally, totally inappropriate to storm up to Olympus and demand that he fight him.
*
Sometimes he loves him.
His visits are few and far between but when he does visit he lights up the rest of Nico's week (month if he can stretch it out- he needs to make these visits last). Because he's still funny and still sweet and still, to use Annabeth's terminology, a Seaweed Brain and other than the occasional story or the odd namedrop (yeah, I was talking to Hermes about the same thing) he's still the same. He teases Annabeth and he stands up for Nico's hair or clothing or whatever is the cause of their current fight and everything is so much better around him.
Annabeth lights up around him, too, eyes shining and he never mentions the fact that they're living together, now. They do totally mundane things such as walk in Central Park and go see movies and just hang out as if they were actually normal people and not two demi-gods and a man who lives at the bottom of the fucking sea. And for awhile they're happy and Nico can remember the Old Days and fighting Kronos, which wasn't exactly a Kodak moment but was certainly a time where they were, you know, together. And maybe they weren't the happiest times but they had a future, then, a definitive future where they grew old and they were all together and Nico was still probably wearing skinny jeans in the nursing home.
When he's there it makes it better, knowing that future will never happen, because what does it matter if he's there, with them? And Nico can forgive him for not being there a lot- he's a god. He has things to do, because there are killer sharks roaming the ocean and Tom Hanks is trapped on an island somewhere and he's doing his best. The gods aren't perfect- most times he thinks they're more fucked up than everyone else. But he's trying.
Annabeth stares at him adoringly as he tells a joke and he wonders if it would be totally, totally inappropriate to grab his hand and beg him to stay.
*
Sometimes he hates him.
Like when he leaves, after sweeping into their lives for a few days and expecting them to drop everything because he's there (they do). After he makes everything better for a little while and then disappears again, off to fight battles with all those things in the sea and do godly things and they're left to fend for themselves. After he leaves Annabeth sleeps on the couch for an undetermined amount of time and she won't touch him or look him in the eye and it's just another reminder that she will never be completely his. It's kind of alright, anyway, because he doesn't want to touch her either because everything about her is just him in a different form, because he loved her before Nico ever did and she loved him first, too, and she loves him still, loves him more.
He thinks maybe he loves him more, too. He doesn't know what the fuck that means but it's there, suffocating him and Nico has a built in death radar and he knows he's not actually dying but it sure as hell feels like it. And he hates him for what he's doing to him and what he's doing to Annabeth- for that sad look in her eyes that never really goes away and those scars on her body that she got from fighting with him, for him, and those scars he can't see that she got when he turned immortal and went off to live in the ocean.
He loves Annabeth but he loves him, too, and sometimes he thinks about what would happen if he ever had to choose between the way things used to be, with him alive and mortal and next to him, to how they are now, with Annabeth sleeping next to him and her smile that's (almost) his alone and he realizes he doesn't know what he would choose.
It's pretty good luck that he'll never have to.
Annabeth sniffles next to him and grabs for his hand because she needs support right now and she'll have to settle for the next best thing, and he wonders if it would be totally, totally inappropriate to wipe his memory clean of him forever.
*
He always misses him.