Confess your love to Seiori before the second act starts. Then choose Natsuki for the weekend and Yuri after. Thanks to this, you will see cut-scenes for each of the characters for the current day. Each of them must be dedicated to write two poems for each girl - Yuri, Seiori and Natsuki. First, make sure there is room for three saves.
The ending will be much better if you act as follows.
