Both classical and operant conditioning are clearly in play when it comes to porn usage.

Operant conditioning is a theory and method about how people change behavior. It's based on the idea that people do thing that bring pleasant results and stop those that don't.

Gregory Razran, Operant vs. Classical Conditioning, The American Journal of Psychology, Vol. 68, No. 3 (Sep., 1955), pp. 489-490 ...