What would you think about a NPC who joined your party, only to realize at a certain point they were spying on you? This person takes you to the enemy which is when you find out their true motivations. But they may forsake their master if during your travels you made the right "choices", in other words good alignment choices. But if you didn't make the right choices, this person would leave your party and join your enemy.
Even if they stuck with you, would you still consider keeping them in your party?
Even if they stuck with you, would you still consider keeping them in your party?