Please note: Nirvana In Fire is NOT adapted from a BL novel. 

The author (Hai Yan) of the book 'Lang Ya Bang' is also the scriptwriter of the show and kept about 90% of the original story intact in the drama.

For more information about the author, novel and drama, please see link here:
https://yingtaoblog.wordpress.com/2015/10/27/琅琊榜-nirvana-in-fire-lang-ya-bang-english-translation-overview/ 

To read the english translation of the novel you can find the translated chapters by the various translators here: https://www.novelupdates.com/series/nirvana-in-fire/