If someone could help me: I'm still missing the second Evelyn/Callie threesome, and I have no clue how to get it. I got Callie on the romance path, same for Evelyn, and I even let them get it on a few times alone before introducing myself into the mix (IDK, the idea was to let them build their relationship before expanding to a full ménage à trois), but it just doesn't go anywhere.
Also, this last playthrough was literally the first time I ever got the Primrose sex friend route unintentionally, and I'm not sure where I messed up.
The threesome with Callie: the final scene is when Callie wants to take it past casual sex to romance. You need to have told her it's more than just sex the first time you got her to have sex with you. I am not sure what else is required, but it's some combination of: spending more afternoons with Callie in the shop, going to Callie for more threesomes, and possibly waiting a few days after you've hit the required number of either or both of those. Also make sure you've talked to her. Sometimes she needs to talk to the main character about the first threesome before things can advance.
Primrose: she won't ask the MC to become her boyfriend unless he's cleared her name before the 7 day deadline. If that's been done, then it depends on how much she likes the MC. You need to have read the book that she's also read, and you need to have worked in the library and read with her in the library enough times. If you spend the first week working in the library in the mornings, and then read the smutty books with her in the reading room, that's usually enough times.
I have seen indications in one of the walkthroughs that acting pervy towards her on day 1, and asking for her underpants before she's ready to give them, can hurt her opinion of the MC, requiring you to spend more time in the library than otherwise.
And, of course, you need to have accepted her invitation to come to the library at night and said yes, let's become a couple when she asks.