The writers should just embrace "duel-protag" which IMO is what this game already is. Let D, Elena and Jen go on a girls night out or something. Just D by herself without F around, sort of like when she went to the beach with Olivia. Doesn't even need to be sexual, just something to advance D's relationships with the other girls, so when those girls join the harem, it doesn't feel forced or unnatural.
I sort of agree with consequences, but this game has never had any consequences besides the gameovers in the first chapter. Obviously NTR isn't going to happen and D isn't going to leave F, but it'd be interesting for D to find out F is banging Elena on the side and they have a fight over that. D was honest (somewhat) and F wasn't, then they can have make-up sex or something.
F in this game is actually a pretty bad dude, mainly with his banging of Elena behind D's back. That isn't that much better than Rachel banging Frank, it may even be worse. MC is D's dad and lover, banging her best friend. Rachel is her mom banging her ex-boyfriend. Yeah, it's probably worse.