A plausible diagnosis for Kemper, could be Social Anxiety Disorder (Social Phobia). Kemper had a fear of social situations with women. After picking up women, he would get anxious in the situation of having women in car with him, he wasn't sure whether or not he would be able to even communicate with them, and was constantly worried about what that thought of him. Kemper did tend to avoid women, aside from when they were in his car. Kemper tended to avoid situations with women specifically.