Yes you can just quit or close the browser if you are into online gambling. But I know that it's hard to press the close button when you are hitting the day badly as you lose a lot. You just have to force yourself to quit and stand up on your seat so that you can just leave the game and have a peace of mind to gamble again tomorrow.
The problem is that when you are having a winning streak, you want to keep it going and if you are on a losing streak, you want to try to get it all back. There's no easy way to get out. You just have to set limits for yourself to get out at a certain point for a loss or a win.