How many times have you said that to yourself? usually we only say this when we've already lost badly. Once we've lost control and a significant amount of money, we regret our actions and promise ourselves we won't gamble again. We tell ourselves we're done gambling to avoid repeating the same mistakes.
The key maybe is to not say it to yourself but to let other people know about it too so that they can offer you support when needed. You can also let gambling prevent you from ever going back. Wanting to quit gambling will be hard if you are the only one you can betray. But if your family and friends know that you are quitting then you might want to think twice before coming back.