Hades and Persephone accidentally sharing his memories and learning how his former wife, who he had mutually had been very much in love with, died. Persephone feels pretty mournful, not only over that, but the fact that she has never experienced such love.
Hades' whole backstory. Guy saw his father violently rape his own mother, then swallowed both him and his brother Poseidon where they had lived in his stomach for years, then after they get out, his youngest brother Zeus decides he's the leader since he saved them and grows up to become King of the gods and gets all the love and glory. On top of that, the only love he had known died tragically, which is what finally pushed him to become evil.
The very last straw for Hades was when he told the other Gods that Leuke was dead. None of them cared, some of them didn't even know he was seeing her and Zeus in particular just laughed and told him she was "just a nymph" and that he can "always find another". Hades had just lost the love of his life and his own brotherrefused to take his grief seriously.
Hades' response to Hermes confirming that the other Gods think he raped Persephone. Given that Hades, due to witnessing the rape of his own mother at the hands of his father, absolutely abhors rape, he's not only furious at the insinuation, but even more hurt and angered by the fact that most of the Gods (except Hermes) believed it.
Hades: You have got to know that is not true! Not me! Not ever!
Hades making Persephone leave the Underworld forever, or so he thinks. They're both heartbroken.