Look, even a materialist engineer like me can see what's staring you in the face.

Rambleaway is a sex- compulsive. He is afraid of making attachments. His partner at Serrydown/ Brummagem/ wherever Fair takes this as a challenge, like women seem to do. He is afraid that he might care about her, risking attachment and (in his mind certain) subsequent rejection.

I'll leave the psychologists among you to work out the details.