Haikei Mishiranu Dannasama, Rikon Shite Itadakimasu

At sixteen years old, Byletta was married off to Arnald, a nobleman’s son with a reputation for being both ruthless and handsome—although she hasn’t seen him once in eight years. Thankfully, Byletta is a strong, independent woman, who don't need no man! When the empire's war finally comes to an end, he returns home as a distinguished army commander...so Byletta takes the opportunity to request a divorce. But in response, he proposes a wager that'll keep them together for one more month. A clumsy love story unfolds between a young woman with the reputation of a villainess, and a young man who has never known love!

[From Yen Press]