Unfortunately, that's the same voice that cries out for booze or drugs in substance abusers.  The very same voice, the one that wants another hit, another drink, wants to fuck, wants to overeat, whatever.

The question of knowing when to stop is a tricky one.  A lot of addicts first find themselves in the position where they think they should cut down on whatever it is they think has gotten out of control.  Gamblers try to gamble less, or make smaller bets.  I would suggest that if you've reached that point, you've already got a problem and stopping altogether is the only--and ironically the hardest--solution.

This isn't true for 100% of people, but it's certainly true for the majority of them, I'd say.  I've dealt less with gamblers than drug addicts and alcoholics, but your brain sees all of it as intense pleasure and craves whatever it is that's your drug/behavior of choice.  If you've realized you have a problem with gambling, I would strongly suggest quitting if you're able.  Also, I'd recommend NOT hanging out here in the gambling discussion section, or at casinos, or in any place that will cause you to want to gamble. 

The memories you formed from all the good times gambling are burned into your brain like nothing else.  Everything you associate with gambling has the potential to trigger you to gamble again--just like drugs.  People, places, things as they say in recovery.  There are a lot of triggers you probably don't even realize.