Infinite
Mortals looked up at the stars and thought the expanse of lights had no end, but Hades had been around long enough to know that even the darkness had its limits. He'd seen stars burn out and be born anew, and if even the vastness of space was finite, it was hard to imagine what didn't end.
Well, almost. As a god in the world of men, Hades knew full well that his time was infinite. Persephone and he had aged over the years, true, but they bled golden ichor, and would not succumb to the ravages of age, disease or war.
But even if he was wrong, if even the gods would one day leave this plane of existence, Hades knew one thing was truly infinite: His love for Persephone.
Infinite time, or close to it, meant that while sometimes they fought, sometimes for years on end, there were infinite chances to reconcile.