There’s chemical addiction and there psychological addiction. Both involve a strong desire to do something that doesn’t benefit or even hurts you. Gambling addiction is a psychological addiction.
I’d even go so far as to say that most chemical addictions start as psychological addictions because withdrawal won’t be that bad after the first time, but you want more because it feels good because most affect the dopamine pathway, some acting as dopamine itself (like cocaine), some increasing your sensitivity to it (don’t know of any that do this but theoretically it would result in the same), and some encouraging your body to release it more readily (like meth).
Though porn and sex addiction (and heroin) might work on a different pathway, as I’m not sure if the orgasm hormone is dopamine or something else, though I do think that dopamine is involved in getting people engaged with sex before the orgasm. From some quick reading, it sounds like dopamine is involved.