Why was he holding back with the woman?
She's an enemy. Just kill her like you kill everyone else.
I don't care about a troll who doesn't pay for his opinion telling me how to review movies.
which one? the bad/evil girl or the doctor?
I assumed the bad girl.
The bad girl said something like they were lovers, they used to be together etc... So he doesn't want to kill her.
But, again it was just an exposition rather than flashbacks. A poor attempt to add drama in an action scene.
------
People only want to hear what they want to hear