I dont read shoujo or romance novels but I recommend reading 'Got a fake job at the academy', the MC in this have long black hair.
only korean romance novels with yandere male lead? : I know some with short white hair, but not long white hair (probably some BL ones exist though) or is any type of novel ok? : japanese, non-romance: The Heroic Legend of Arslan
not exactly long hair but "How To Win My Husband Over" is a good novel with white haired ml also I remember the ml of "I Was Discovered by the Villain" havving long white hair in the manhwa? only a few chapters of novel are out so I haven't started it