To Sir, Without Love: I'm Divorcing You I, Part 1 (light novel)

A MARRIAGE ABOUT TO END BEFORE IT BEGINSAt sixteen, Byletta Holland was married off to Arnald Swangan, a nobleman’s son with a reputation for being both ruthless and handsome—who also left for the war front on their wedding day. Eight years later, the war has come to an end, and Arnald returns home as a distinguished lieutenant colonel, while Byletta has built her own life without him. When she takes the opportunity to request a divorce, he proposes an unbelievable wager: they sleep together for the next month, and if she doesn’t conceive by the end of it, she gets her divorce. Between Byletta’s notoriety and Arnald’s inexperience with love, is there any hope for this pair?