Watching porn certainly does not indicate one has a problem with porn or sex addiction. An infidelity does not indicate sex addiction. How can you identify a problem or this much misunderstood addiction? This is a very direct, down to earth article about the signs and symptoms you might want to see a Certified Sex Addiction Therapist (CSAT) about.
http://www.thefix.com/content/7-signs-you%E2%80%99re-dating-sex-addict70002