Percy was overjoyed when he saw Annabeth under that parking lot. He thought that it was about time they got together again. After all, with Gaea, the previous war, and not to mention Hera, they barely had time for each other.
So when it was time to board the Argo II, Percy just wanted to skip all the way up the rungs of the ladder. They found the statue of Athena (Annabeth did that, but still). They defeated the giants. They saved Nico. Everything was going as he had hoped. But naturally, a demigod shouldn't push his luck. And that is exactly what Percy did. So when he looked back, fate already had something planned for Perseus Jackson. Usually, when fate is involved, it isn't anything good.
The small smile vanished from Percy's lips and was replaced, not with terror, but with a tired look. Honestly, who wouldn't be sick from all the gods, giants, and monsters? But Percy was never one to get depressed. When he looked back and saw Annabeth slipping away into a massive and terrifying hole, he jumped and grabbed her hand.
Percy thought nothing could suck more than being away from Annabeth for months. Apparently, fate liked to prove him wrong. But Percy, again, was never the type to back down. So when fate (well, more of Arachne) said that Annabeth was coming to Tartarus, Percy couldn't help thinking.
Screw you, fate.
He grabbed Annabeth's hand and didn't let go.
Never again.