Well, I could agree with you for Sage as a fuckbuddy, maybe Bella too, but we should also remember and take into account what Elena says to the MC just before the big choice at the end of episode 8, where "if it didn't clicked yet after going through the end base, it's probably not meant to be", where the MC own wishes is to clear his head on where he's at on his love affairs, the MC respects both Sage and Bella, he cares about them, and doesn't want to just "use" them, he has the opportunity to chose Sage or Bella if their path are still active, so in the case you chose Others while Sage and/or Bella were options, it does mean you're not chosing them, so yeah, prefering to end it with them kind of makes sense since in that case, as Elena advised, it would only make things worse with time. But yeah, maybe if you're a massive DIK, you don't give a fuck and keeping fucking them for the sake of fucking them without the feelings, could make sense, but with the "care about them" into account.... For the Sage path at least, the game does show you the door isn't completely closed in the future