On the left side of the screen is the Link Gauge, which changes during the course of the game.
It moves according to your choices, including your responses during dialog sequences and which events you choose to participate in. Where the gauge rests will also affect the outcome of certain events in the game.
The choices you make will affect not only how the story develops, but how much each one of the heroines likes you.
Certain events will not happen if the Link Gauge is not in the right place...
While there are no "right" answers, your choices affect the Link Gauge and Affection simultaneously, so while one choice may increase the Affection for the heroine you like, that same choice may push the Link Gauge in an unintended direction.