Another promising title that showed up while I was gone, A Man of Genius by Janet Todd:

A Man of Genius portrays a psychological journey from safety into obsession and secrecy. It mirrors a physical passage from flamboyant Regency England through a Europe conquered by Napoleon.

Ann, a successful writer of cheap Gothic novels, becomes obsessed with Robert James, regarded by many, including himself, as a genius, with his ideas, his talk, and his band of male followers. However, their relationship becomes tortuous, as Robert descends into violence and madness.

The pair leaves London for occupied Venice, where Ann tries to cope with the monstrous ego of her lover. Forced to flee with a stranger, she delves into her past, to be jolted by a series of revelations–about her lover, her parentage, the stranger, and herself.