That's my main and only grievance with this game. (WARNING: impending personal kink championing). It would've been easy to make the FxF route a sustainable sideleap able to woven back into the main storyline. Sure, some scenes would need alterations, the whole "drug addiction" shit would need some serious downscaling (if not a complete removal), and the "dominant VS submissive" variables could be simplified (or removed completely) for the sake of easier absorption into the main storyline, but the point stands. If SG wanted to, it would've been 100% doable to make FxF NTR a sustainable and continuable part of the game. Also: I really, truthfully, honestly, wholeheartedly, earnestly, genuinely despise "you chose wrong. Now go back and do it the correct way, deviant" bad endings. It's lazy storytelling, and more often than not they feel like an insult and a slap to the face.
Bad consequences > Bad endings