If a herbalist said she could save you, and all you had to do was promise to marry some rich, eligible bachelor, it would be a no-brainer. Sign me up, a young heroine might say.
So, Vivian Darius promises to marry Lord Everleigh. Not a problem, she thinks, because she isn't expected to live.
But then she gets well. As her health improves, it's time for her to make good on the promise, except he didn't agree to anything, except a kiss...
Writing these characters is what makes writing enjoyable, and seeing the twists and turns as the story arrives on the page. When you begin writing, you've made a promise to the character to make sure she gets her happy ending. Then, on publication day, it's official.