Assuming bisexual Nico (which I love to occasionally do) (boy had a years-long crisis over hopelessly loving a boy, you think he even paid attention to anyone else long enough to realise being bi is a thing at all?), Nicobeth has so much potential for angst and good storytelling…
Just imagine the possibilities.
Percabeth break-up and bonding over the boy they both tried and failed to be loved by.
Mutually worrying they might just be on the rebound because they couldn't imagine loving each other.
Crisis of faith I mean sexuality for "I still have trouble accepting I can love men" Nico, overly factual Annabeth trying and not succeeding at first to explain bisexuality to him.
Realising an emotional bond between them and struggling to find common ground for a relationship: team-oriented Annabeth vs. loner Nico, optimistic and solution-oriented Annabeth vs. pessimistic Nico.
Annabeth's hubris making her think she can get him to open up and almost driving him away with her attempts. Nico's nihilist attitude almost driving her away because he's convinced he's going to fuck it up anyway. His impulse to run away nearly messing up everything early on.
Maybe featuring bisexual Annabeth who's got anxiety thinking after two failed relationships with men, she's just not cut out for heterosexuality.
Maybe Nico not getting bisexuality at first, hearing some nasty biphobic tropes, and breaking it off because he's convinced this means he will be a cheater.
(And that's nothing to say of Percicobeth, a related but entirely different can of delightful worms.)
P.S: Percy dying, both of them having an impulsive affair, both feeling guilty and like they're disrespecting his memory, and working through that!