「涅槃で」って、何といういみですか？

Subtitle interpreted it as 'why'. Googled it but haven't got a clear explanation.

https://preview.redd.it/p22svmnka4gd1.jpg?width=1178&format=pjpg&auto=webp&s=b5ee4ae9d49fcc339843eeaec145fd05345b8214

https://preview.redd.it/emug17oka4gd1.jpg?width=1222&format=pjpg&auto=webp&s=41fe7e355fd6426754c448a3add1f94177a8988c

Sounds like '(Why) am I dreaming of you BEFORE MY LAST BREATHE【涅槃で】?'