Self-Control: A Novel (version 2) - Mary Brunton

Laura Montreville is a well-born and religious girl, brought up in Scotland by her widowed father. She is pursued by Colonel Hargrave, a libertine, who makes an offer of marriage which Laura, not knowing any better, declines at first, saying she will marry him in two years time if he reforms his wicked ways.
The book follows the fortunes of Laura, who suffers impoverishment, illness and humiliation, all the while tormented by Hargrave who has no intention of waiting the stipulated two years and who eventually shows himself in his true colours. - (Summary by Simon Evers)