I've always found the love triangle device gets dismissed as melodrama, but in historical romance it can be a razor-sharp tool for exploring social constraints. Take 'The Winthrop Woman' by Anya Seton. It's less a clean romance and more a sprawling biographical novel, but the protagonist’s torn affections between a passionate rebel and a stable, respectable man mirror the entire conflict of the New World. The drama isn’t just who she picks; it’s the cost of that choice in a society where a woman’s name and security were everything. The historical weight makes the personal longing so much more desperate.
For pure, unadulterated drama on a grand scale, you can’t beat 'These Old Shades' by Georgette Heyer. The central triangle is magnificently messy, built on disguise, revenge, and twisted loyalties. The tension comes from the constant threat of exposure, not just of feelings but of identity. Heyer’s wit keeps it from being maudlin, but the emotional stakes feel sky-high because the characters have so much to lose beyond their hearts.
A more recent read that fits is 'The Lions of Fifth Avenue' by Fiona Davis, though it’s dual-timeline. The historical thread involves a librarian at the New York Public Library caught between her duty to her family and a radical journalist who represents intellectual freedom. The drama is quiet, internal, and devastatingly real. It’s not about ballrooms and dukes; it’s about a woman trying to carve out a self in 1913, and the love triangle is the crucible for that struggle. That kind of drama lingers.