The Duke’s Diary by Ashtyn Newbold

She only meant to read one page…until she saw her name.

Rather than being forced to marry the vile man her father intends for her, Nora Rothwell plans to escape. With the help of her brother and his best friend, Timothy, the Duke of Heywood, she finds her way to the Duke’s abandoned hunting lodge, where she will be kept safe and hidden until she comes of age—at which time she will be whisked off to London in the hopes of finding a suitable match who might secure her a place far from her father’s reach.
Secluded from society, Nora enlists Timothy’s help as she prepares for her London debut. Ever serious and unromantic, he teaches her the essential skills of catching a husband, leaving her with no question that he sees her as he always has—a friend, a child—perhaps even a sister.
But when she discovers an old diary in the library, everything she thought she knew is called into question.
It’s Timothy’s diary.
And if its contents are to be believed, he isn’t unromantic in the slightest.
…and he most certainly doesn’t see her as a sister.