After the Reunion, the Ex-Husband Proposed to Remarry Step by Step.

The male protagonist doesn't necessarily love the female protagonist very much. When the female protagonist proposes divorce, the male protagonist agrees without asking why. Later, he discovers that the female protagonist has become a partner. The male protagonist then realizes that he loves the female protagonist, so he begins to investigate everything that happened to the female protagonist, and then puts the blame on his adopted sister. He has no responsibility at all. (｀_´)ゞ