Hm... it's not a matter of being mean or nice to either one, but it is possible to get locked into the bad ending at the final option if you pick certain very specific choices, which honestly, is more difficult to get than the safe end.

Is that an older version of the game? Cause that might be one.

Another is your first choice when you meet Edel (the one with the very first CG). If you choose to ask about the boss, it makes everything harder for you.

Another is if you never snitch on him (you should).