Ok, I was getting agitated with FL being romantically stunted (like he's being very obvious about his feelings though he hasn't flat out said it) and also refusing to clear up the misunderstanding. However... After reading the spoiler, I can fill in on how we got to this point with the sister and whatnot. It's just frustrating being to that point in the plot
Why would she even know where the bottle was?
That mad scientist may have left her hints intentionally or accidently. Plus she is a scheming little bitch, so that probably contributed...