While sex addicts definitely have some narcissistic traits, true Narcissistic Personality Disorder is quite rare: generally, it is thought that 1% of the population meets the diagnostic criteria for this disorder, though some put the number as high as 6%.
But diagnostic criteria aside, sex addiction is a selfish behavior/addiction. Though sex addicts don’t set out to find a way to be selfish and hurt those they love, the result of this addiction is a selfish drive for their next “fix.” And the secrecy and broken promises that are a part of the addiction do bring trauma into the addict’s family’s lives. But even when the addict wants to stop his hurtful behavior, because of the psychic hold this addiction places on the addict makes it incredibly difficult to break free of. Even addicts who love their families deeply find the addiction very difficult to beat.