Gambling can be stopped with will power and self control. You do not need therapy combined with other treatments, simply act like a responsible adult.
It is not always as easy as you make it seem and you should pray you don't get addicted in something, be it gambling, drugs or anything. At some point, you would think that gambling addiction is spiritual because you cannot just stop yourself no matter how hard you try. I don't know how far will power can take an addicted gambler but I know it is not enough to handle a case of addiction, that is why seeking professional help is always recommended. Although not everyone went through a therapist but it is always better to talk to someone about it as that will produce faster result than handling it alone.