where his civilizations, including our own

The "gleam" in Dumbledore's eye was because once Voldemort took in the oxytocin from Harry's blood in order to grow, he also doomed himself to be more vulnerable to feeling actual empathy or remorse (other effects of oxytocin), which "doubled" the connection between Harry and Voldemort because now Voldemort *really* identified with Harry, having admitted that he needed love like Harry had received in order to grow. So when Harry said "be a man... I've seen what you've become... try... try for remorse," he was the only person in the world whose words could actually *reach* Voldemort, and Voldemort knew, by that point, that Dumbledore's words were true: that there is something worse than death, and that is to feel remorse for crimes if you've committed crimes as bad as Voldemort's. So he refused Harry's offer and felt death because it was the less painful option for him. It would have been more available to him had he stopped committing crimes sooner, but he had so much damage on his conscience (= his soul was so fractured and unstable) that he wasn't able to withstand it.