He doesn't have anything to say to that. She chose staying in Hades over being with him once before, too.

It's only one day, and he'll have to go a thousand more lifetimes without her.

It's a whole extra day with her. He never thought he would get one more day.

After a while of sitting there, just holding her, he starts quietly singing. It's a song from when Ariadne was alive, one of his favorites from back then, about springtime, and trees growing, and one particular verse about two goats who are in love.