OP, I don't think that your friend quitted gambling, he went on break and didn't quite. Gamblers are used to going on break after a huge loss because they feel that's the best way to avoid more losses. However, after a while, the gambler can start considering to gamble again in order for him to see if he can win back his losses. This is the reason why, when gambling don't think of profit in order to prevent you from making wrong decisions.
Quitting gambling means you stop and never gamble again. If his friend gambles again, it means he didn't quit, but the one closer to this is that he rests for a while to get rid of frustration due to losses. Because sometimes that frustration can lead to revenge bets and addiction that you can't control if you continue to gamble.
So the only solution to avoid this is to take a break or rest a bit and go on vacation. It should drop your addiction to gambling and help you think that gambling is for entertainment purposes.
We shouldn't gamble to double our money because everything in the casino is based on luck; no matter how hard you pray, the result will still be based on your luck.