Tsuma no Haha Sayuri

妻の母さゆり

The main character is a white-collar worker. He has a wife, but she runs away from home. When he is at a loss what to do, Sayuri, his wife's mother, reaches out for him, "I'll replace her... Please..." As he lives with her, he gradually falls in love with her, and so does she... (Source: VNDB)