Nico di Angelo
In The House of Hades, Nico is forced by Cupid to reveal that he had had a crush on Percy Jackson. This reveals that he is gay. In The Blood of Olympus, he later says that he does not feel that way anymore about Percy, and that he had been young and impressionable at the time, (by saying Percy is "not his type") and is seen to be potentially crushing on Will Solace (head counselor of the Apollo cabin).