The worst part of the curse isn't when they're there. It's when they're gone and she spends what seems like eternity waiting and watching and wondering.

Each one of them has promised that they'll come back, but none of them have.

She learns later that Percy tried, but forgot. She calms herself with the curse that she sends his beloved when he leaves. She loves him too much to punish him, and she hates Annabeth.

The one who comes back isn't her knight in shining armor, but he came back and that's what matters. Calypso has found love in imperfection.