To Sir, Without Love: I’m Divorcing You, Vol. 3 (manga)

The Swangan country estate incident may have been resolved, but Byletta has a new concern—her husband Arnald’s gaze upon her grows sweeter by the day! Where did the ruthless, cold-blooded man she’s heard so much of go?! Byletta’s rather doubtful of whether she can open up to the very man who proposed such an outrageous wager.
And when an old adversary at the victory celebration maliciously lays Byletta’s past bare, will Arnald believe in her honor or will the couple’s budding relationship wither?