I genuinely don't care if I'm called a conspiracy theorist for this, but - there's a reading which could support gay oriented aroace Nico.
We know he "gets over" his feelings for Percy at the end of BoO - almost by conscious choice - something along the lines of "Percy no longer looked like someone to idolise or crush on". Now if it was this really deep romantic crush - supposedly for years, he most likely wouldn't have gotten over it - certainly not by conscious choice atleast.
Now, there are pretty clear Doylist reasons for it (setting up Solangelo), but I choose to take creative liberty with the watsonian reasons - both of these make sense:
a) Nico is a grey-aro and asexual who took the the crush to be deeper than it actually was OR
b) Nico is a gay aroace who may be homo-alterous/homo-platonic (or both), and his feelings for Percy happened to be a strong alterous/platonic crush.
If you're inclined to believe the second aspect, it's not very hard to write off an alterous crush/platonic one as romantic - it's fairly common with aros. Nico, after all grew up in very amatonormative/allonormative times without information or vis- having romantic feelings for men was bad, but not having any romantic feelings was off the table.
With regards to the Cupid Scene, if we're taking the second interpretation, cupid is the god of love - and the thing with love is that it comes in all kinds. Or what if Cupid, being sadistic and cruel as he is - chose to nudge Nico deeper into his misgivings?
I believe his feelings for Will were also either a shallow romantic crush or alterous in nature.
I know everyone attributes the "don't call me boyfriend" bit to internalised homophobia, but what if Nico didn't want to be called boyfriend because for him, they weren't dating - in his head it was a qpr but he didn't have words for it?
I could read his crush on Percy as a shallow romantic one, and the one on Will as alterous. Or both of them as alterous, or both of them as shallow romantic ones.
Anyways, I'll always see Nico as asexual either way: if he's aro or homoromantic.
I know this is wild, but if there is a bizarre, highly unconventional reading of canon I like, I'll run with it. Don't mind me :)