Watashitachi, Rikon Shimasu

"Before our next wedding anniversary, we should get divorced."

One night just before their third wedding anniversary, Kazuomi's wife Sayo suddenly asks for a divorce. He is dumbfounded by her sudden request, but Sayo simply smiles and says, "Let's just act like we usually do, during the rest of the time we have together." Her behavior causes his heart to drift away, but there's a secret that she's been hiding from him. This is a heartfelt and tear-jerking romance that revolves around one couple's marriage and divorce.

(Source: MangaPlaza)