User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-4430596-20121009003401/@comment-3146930-20121010210232

He may not have. Annabeth simply said that she thought he had a crush on her when he was younger. However, in The Last Olympian, it is shown that Nico is just very shy around girls (even nymphs), so Annabeth could have mistaken his shyness as a crush.