He never did tell her again. He somehow knew that she would laugh. If the evening hadn't had romance in the air and she hadn't breathed it in; she would have laughed at him.
At the river of Styx he had to choose someone that made him want to keep living. His one and only. And once again she had been the one to save him.
She was always saving his butt. Ever since she had met him she had been saving him from monsters and eternal "doom". That occasion had been no exception. Ever since they met she had cared for him. Why? Percy still wasn't very sure. All he knew was that at the river of Styx she completed her promise to Chiron of keeping him alive.
Maybe thats how. Maybe she knew he would have to go against this task so she seduced him into loving her. She gave off that adorable smile to save him and make him feel proud when he didn't deserve to. And slowly by her hair tickle his face when he walked by to giving him a kiss on the cheek when they won their chariot race, she pulled him in. Maybe this was her initial plan. And maybe, just maybe, she fell in love herself.
Sure she would tease him for loving that loving moment in which he finally admitted to himself that he loved her. In the face of death, he had finally somewhat figured it out. And no matter what she would say to him it was still one of his fondest memories.
Other than you know, their wedding and their son being born.