Maybe you should find some hobbies, try playing some sports, go to the gym or something like that, if you cant stop maybe you should go to the doctor, if that dont help you and you sitll gamble, try to set limits for you how much are you ready to lose this day, try lowering your amounts every day.
Join marathons or be in a riders club. There are so many ways to leave gambling but don't take it so quick, just do it a little by little and take your time. You don't have to rush, give it maybe 15 days is enough for you to have another practice. Lowering the amounts as he gamble can help somehow but still he has to be serious if he wants to quit and he should stay away from any of it.
By quitting it quick people may think its easy come easy go but it is not like it. Every habit is not easy to leave and especially when it becomes addiction. The only thing that can help anyone to stand for to leave gambling is the will power. Usually we say to avoid it by keeping yourself busy but it can only help in the initial day, after then you have to make your mind that whatever if happens but you will never go back for gambling. The only remedy to addiction is to make yourself strong, there will be a continuous fight of your will power with the addiction at any moment a weakness of will can harm you mission to the failure.