I believe “sex addiction” is a made up “disease”.
Not according to my wife...
Actually, people can become "addicted" to anything. I believe the manifested 'addiction' is likely a symptom of an underlying problem. I'm no doctor or anything though. Just my guess. (this is not to be confused with chemical dependence.)
Heck, people can be 'addicted' to chocolate, caffeine, nicotine, opiates, sex, and many many many other things.
I think the commonality with all addictions is endorphins and or Adrenaline in the brain. People probably latch onto it due to an 'emptiness' of some kind in their lives, or perhaps a chemical deficiency. Who knows...