Sex addiction is a controversial label for someone who feels that they cannot control their sexual behaviours or fantasies. It is controversial because many people feel it isn't a diagnosis in and of itself but is a symptom. I agree with this, though clients can find it useful term to help them find help. I do not label people addicts and also believe that behaviour can change if the person is open to it and can work through the underlying causes.
When I work with clients who feel they are compulsive, it is often not about changing the acts themselves, rather helping the person to feel in control. For example, if someone is spending all their free time watching BDSM porn, they might want to learn about places they can meet other kinky people or how to bring up these preferences with a partner.