I bet the guy started out in different areas to release his tension, get his kicks, etc (




or prostitutes) and then escalated to real women with his spree. I think he may be both repulsed and excited about killing Brianna. I don't think he went to that level and won't go back. He appears to be methodical, and believes he has great self-control or self-command, as evidenced by his grooming habits, IMO.
I think he has returned to whatever he did in the beginning, thinking he can master his impulse. I'm sure the guy is a bundle of nerves in real life, trying very hard to show self-control in his daily routine, but is having a very active fantasy life.