I did not know there was affection level in the game. Is this only for Jill and is there a way to check the affection level?
Regardless, maybe you should add skills and/or passives that're only for Brookes and Jill after reaching certain affection level and maybe have a special conversation between them. Also, maybe for near the end of the game, something could happen between Brookes and Jill if their affection level has met the condition or not.
I just thought of those ideas after knowing affection level is in the game.