Nicki is looking for this one! And it’s a jaw dropper, however the big twist is revealed in this question below so tread carefully if you hate spoilers.
This reminds me of one of my all time favorite books about mental illness with a huge plot twists that rocked my world (though I know for sure it’s not the same one).
She asks:
Looking for an old favorite. I read a romance book some years ago.
The h in this novel is mentally ill (I think she’s undiagnosed and doesn’t realize???). I’m not sure.
Real