Actually it can be a thing of decision, if a gambler decides to stop, it would literally be very difficult for him, it's just a matter of time and determination. The gambler should see it as a thing that's not beneficial. As time goes on that gambler tries to forget about it and also trying to concentrate on other important things that would be more beneficial. Gradually he/she would forget and move on.
It is possible for it to be a thing of the past
Of course things like gambling addictions can be overcome and it can become possible for it to be a thing of the past, but thats easier said than done. In reality most people need some kind of outside help when overcoming their gambling problems. Self help is really only going to bring you so far before you realise that you lack the discipline (as most people do) to go through with it.
Addictions are unfortunately a long term brain hormone disbalance. So "forgetting and moving on" is reallly just a fairy tale. That takes years.