The way the characters and their relationship is explored through choices is very promising. I think Alex's suggestions are on point: using the relationship as the basis of the game mechanic, aided with variables, has tons of potential. Consider, for example, the use of variables that are communicated to the player vs variables that are hidden. For example, the main character could have a $shyness number, which can be shown and managed openly. On the other hand, you could also have a variable for Leo called $interest, that is not shown as a number, but increases or decreases with player decisions. Then you can use (if:) statements to reveal new dialogue options or entire passages based on $interest. Just an idea. Keep it up!