This is the type of game where you will need different saves, the paths split early, each girl has a solo path although some aren't considered 'main love interests' for example Cassie I consider a
side chick You and her are just
having fun after all.
You can have an experience with Cassie and Cindy but this is not considered a regular thing - not like the Louise / Danielle path is - that's more official. Cassie and Cindy happen due to Cindy's interest in the MC, and your interest in Cassie and a specific side of Cassie's character being
present.
There is no
downside to going after other girls while staying with Louise (aka the supportive path) Though if you pursue one, you shut off another (for example going after Danielle will lock off the Kimiko Path, this is due to the two of them being exclusive of each other).
In order for the Cassie / Cindy stuff to happen, you need to reject Louise. Kimiko's content can occur with or without Louise, though you lock out Danielle's path (and by extension Cassie / Cindy as well).
During the 'drinking' game at the beach house you used something she said to you earlier in the evening to force her to drink. It's not a negative... yet