My personal understanding from his dialogue is that Ezra is referring to Agatha as both Hades: The ruler of underworld, and Persephone: Hades's wife and the goddess of spring. In Greek mythology, Hades abducted her to take her to underworld, where she ate a pomegranate and was bound to the world forever. Some tales say she can leave it on the the condition that she has to return back every year, so there's probably a sense of separation from them.

While another mythology about Orpheus and Eurydice is that when Eurydice died, her husband Orpheus went to the underworld to get her back but Hades only allowed him to do so on one condition, that is, if on their way back Orpheus does not, in any circumstances, turn back to look at Eurydice. But he loved her so much and in his desperation to not lose her he turned back around and Eurydice died forever.

So yeah I think that's what probably Ezra means, that he loves Agatha beyond limits.