My exabf a crack addict, was not a cheater...thought it was wrong and a dealbreaker...go figure.
One of my lifelong friends married two cheaters, they were not alcoholics or drug addicts.
My mother is an alcoholic, has cheated many times.
IMO, cheating is an entirely different issue, drugs/alcohol may increase the impulse level, however, it is either set in ones core values or not.