This Is How I Disappear

When Regulus enters the cave, he knows this is the end. He anticipates darkness and pure, unfeeling bliss, but what he gets is another shot with the brother who didn't care enough to stay for him. Will the two finally reconcile after years of misunderstandings and hurt feelings? Or will they splinter apart for good, dooming themselves to an eternity of unrest? [also on AO3]