Yeah, hybrid werewolf-vampire romance is such a specific itch! It's not as common as you'd think. The one that immediately comes to mind is the 'Night Huntress' series by Jeaniene Frost. The heroine, Cat, is a half-vampire, and the main love interest, Bones, is a full vampire, so it's not the exact hybrid you asked for. But the supernatural tension with the werewolf character, Dave, and the general war between the factions is a huge part of the world. The real meat of that series is the push-pull between different monster societies and their rules, which creates a similar friction.
For a more direct take, the 'Dark Protectors' series by Rebecca Zanetti has a book, 'Fated', where the hero is a vampire king and the heroine is part of a werewolf-enemy race. The lore is intense, with ancient curses and biological imperatives pitting them against each other. The tension isn't just 'will they or won't they'—it's 'can they even be in the same room without starting a species war.' It’s less about the hybrid being a single person and more about the union itself creating a dangerous new hybrid dynamic.
Honestly, you might have better luck looking at shifter romance with vampire antagonists, or vice versa, for that core tension. The 'True Blood' books by Charlaine Harris, the Sookie Stackhouse series, play with this a lot with the werewolf Alcide and vampire Bill/Eric, though it’s more of a love triangle than a direct hybrid romance. Finding a single protagonist who is literally both is a tall order, but the conflict between the two groups is a whole subgenre.