anvil, i think i am using the term addiction more broadly -- to define any compulsive behavior, be it drug use, eating, sex, spending, obsessive thinking.
i also didn't mean to imply that infidelity was the result of drug use. . . but that they do go hand in hand speaks to the underlying issues of the individual. . that cause them to pick up drugs or anything else compulsive in the first place. all these behaviors are an attempt to fill a void and then they become compulsive and detrimental to the user's well-being, but still they cannot stop = addiction.