I can not control my greed in gambling, because I want all at once and more. Because of this, first I lost a lot of money 
You should change that type of attitude because you did saw the result of it and that's not going to be a good thing for you. Don't think that you can get what you want that easy and, all at once? I did think about that too when I still didn't realize that if you won't control your greediness it will bring you close to your failure.
He should completely change his attitude to gambling.
Gambling's main purpose is making fun, and he mainly thinks that gambling's purpose is making money, which is false, as you always loses at the long run against the house.
Once you realize that gambling is a fun hobbie u would start enjoying it instead of suffering from it.