@Kita you don't, and you aren't. so long as you share even a single flash of understanding with another, ever, you're not alone. not until every last soul on the planet and you've forgetten all of them and you've lost all hope of ever finding another again will you be alone. Even when shinji was the only one who chose to remain, he had his memories, and he had hope, and he wasnt alone.
Dont drive yourself mad. it's awfully easy.