You both never left each other's side, even before y'all fell into Tartarus, which just made y'all even more clingy to each other. You both cared and secretly loved each other.

After surviving Tartarus and finishing the quest, y'all went back to Camp Half-Blood. You both went to his cabin and plopped onto his bed.

He wrapped his arms around you and pulled you against his chest, not wanting to let you go. After Tartarus, he was scared of losing you.