My Dear Duchess. Regency Royal 6

Handsome, dashing Henry Wright, the Duke of Westerland, needed a wife in a desperately short period of time. If he could not find a wife, he would lose the legacy he so desperately desired. Young, lovely but sheltered Miss Frederica Sayers needed a husband just as much as Henry Wright needed a wife, only she needed a husband to save her from the life of shame that almost certainly awaited her when she fled the callous cruelty of her family.
Marriage between the dashing lord and this reckless runaway was clearly the answer for both of them - until the duke discovered he had a duchess he could not tame and the duchess found that she would rather lose her until then spotless reputation than lose him to another beautiful woman who was everything she was not.