Thanks for the info. I ended up looking at the image files to see what I missed and it seems that I erred a few episodes ago where I didn't choose the option of wanting Debbie for myself and instead chose to help her out with Lily while also pursuing her and so I didn't get the option at the beach house to choose her (although I did have the options for just Katie, just Lily, and the foursome). I'd have to waste a bunch of time going back just to change that decision while keeping all of my other decisions so I guess I'll stay on my current harem path where I'm slanted more towards Katie out of the 3, but still keeping my options open with Debbie and Lily (but no solo scenes with them in Chapter 20 since there doesn't appear to be a way to do the foursome scene and get those scenes this chapter).
Fun game, though. The writing is a bit odd but this is definitely one of the best games I've discovered on here. Hopefully the harem path ends up possible with all of the plot threads beginning to converge.