Remus Lupin doesn't want to die. He, in fact, wants to live with his new beautiful, unsettling wife and their incredible baby boy. He wants to sing his son to sleep in an awful voice until the kid cries for his mother. He wants to kiss Nymphadora every night before bed and every morning when he wakes up. He wants to endure transformations with her hands running over his fur. He wants the war to end and to have dinner at Harry's house, to tell him all the things he could never bring to say before, all the stories about his parents and the Maurauders and Sirius and his stupid motorbike. He wants to watch James and Lily's son get married and have kids of his own. He wants to be normal and happy with no Dark Lord, no prophesies and no death that isn't entirely natural.
But when the he sees the jet of green light (he never believed in slow motion before now) heading for his beautiful unsettling wife, his thoughts are not of the future but of the past, of the life he had, of everything he has given. In a flash, shorter than one word, than a whisper, than a thought, he knew that his life was all he had left to give. He had given victory his friends and his vitality, his innocence, his youth, his pranks, his laughter, his self-hatred, the fierceness of his love for James and Sirius, his hatred for Snape for making Lily cry. He had given victory everything but himself and so he flung himself in front of the jet of green light with one last thought.
"Don't cry, Dora. It was always supposed to be like this."