For me, LIs are girls who have a pathway and will require either a break from that path or an ending. They are, whether official or not, possible "girlfriends". Within that umbrella term, Main Girls are the five who have interlinking storylines/key involvement in the main (canon) storyline (so Sage, Josy, Maya, Jill, Bella). Side Girls are the other girls who have paths but are not integral to the main story, even if their paths give them a lot of content (e.g., Quinn, Lily, Nicole, Riona, likely Zoey). Lewdable Girls are all the others who you can get scenes with but have no actual pathway (e.g., Camilla, Sarah, Mel, Sandy).