The intersection of dark fantasy and vampire romance has some genuinely unsettling corners. For a grimdark vampire court intrigue, you can't miss 'The Serpent and the Wings of Night' by Carissa Broadbent. It feels like someone took 'Throne of Glass' and dipped it in Gothic tar. The relationship is a slow, painful burn soaked in mutual deception and political bloodshed. The fantasy worldbuilding is dense, with a dying sun and brutal, god-like vampires ruling over humans in a terrifyingly systematic way.
If you want something even less romantic and more focused on monstrous nature, try 'Empire of the Vampire' by Jay Kristoff. It's narrated by a vampire hunter recalling his life, and the vampire lore is deeply embedded in a decaying, almost post-apocalyptic world. The romance element is tragic and destructive, not sweet. It reads like a dark, profane medieval tapestry, perfect for fans of 'The Witcher' or 'Berserk'.
A slightly older but foundational pick is Anne Bishop's Black Jewels series, starting with 'Daughter of the Blood'. The vampires here are part of a broader dark fantasy universe with deeply twisted power dynamics and a pervasive sense of corruption. The romance is intense, possessive, and walks a very fine line, which fits a dark fantasy craving for morally ambiguous relationships.