The dynamic of that specific forbidden love is really grounded in power imbalance, isn't it? It’s not just a cultural taboo but often a literal, physical danger for the human. That’s the core tension in a lot of the darker takes. A lot of people mention 'A Court of Thorns and Roses', and while it fits, I feel the 'forbidden' element gets softened pretty quickly once Feyre is turned. The early sections capture that peril perfectly, though.
For something where the line feels more absolute, 'The Cruel Prince' by Holly Black is a brutal masterclass. Jude is a human in the Faerie court, and the hostility is systemic and personal; loving a fae isn't just risky, it's politically suicidal and feels like a betrayal of her own kind. The romance with Cardan is drenched in that toxicity. On the gentler but no less forbidden side, 'Emily Wilde’s Encyclopaedia of Faeries' has a slow, scholarly burn where the danger is more about losing one’s humanity to the alien, captivating logic of the fae realm. Wendell Bambleby is a constant, charming threat to her entire world. That one lingers because the 'forbidden' part is so subtle and psychological.