Gentle Conquest by Mary Balogh

The marriage of Georgiana Burton to Ralph, Earl of Chartleigh, begins with every promise of happiness for both, though they scarcely know each other. She is attracted by his youthful good looks and gentle, courtly demeanor, while he is dazzled by her beauty and vivacity.
It soon becomes clear, however, that the very qualities that attracted them before they married are driving them apart. Ralph is intimidated by the bright star who is his new bride while Georgiana is dismayed by her bridegroom’s shyness, which seems to worsen with every passing day.
Finally each of them sets out to devise a bold scheme to bring about the happily ever after for which they both yearn. It is only to be hoped that they do not bring disaster crashing down upon their dreams instead.