It does sound as though your boyfriend has already been thinking sexual thought about someone else - either real or on paper or on screen. (thecoupleconnection.net)
Sexual addiction is best described as a progressive intimacy disorder characterized by compulsive sexual thoughts and acts. (myintimcity.com)
We will then seek to discover the hidden causes for your addiction while pursuing solutions that will help you gain control of unwanted sexual thoughts and behaviors. (tacomachristiancounseling.com)