It is best to quit when you start to see signs that it is becoming an addiction. You can notice if gambling causes anxiety, stress, or discomfort. Generally, you tend to have excessive losses, so I recommend you escape from that situation and focus on other things to change your behavior. Generally, if you stop in time, you will avoid falling into addiction and be able to play again in a controlled manner.
The problem is that it's difficult to stop on time when you are making Profit, a lot of addicted gamblers I know got hooked because they made a lot of Profit when they started gambling. Addiction doesn't start in a day, it can take days, weeks and months. When it becomes a repetitive pattern it means that your brain have gotten used to it. When you feel anxiety when you are gambling because you are scared to lose then there's a problem
Honestly speaking i think i was in such position in gambling there is much challenges of controlling ones behaviour when experiencing success particularly in the context of gambling, to be honest i was really not that easy to see yourself making that much profit which is know to be a powerful motivator and this already has make it more difficult for any individual in that position to stop totally or slow down for a bit, to around it up i think as addicted gambler who is suffering to quit once that is really not possible but it a bit of time and the process beings infact trying to back at onec can sometimes lead to mental illness which could be as well as harmful to the body of the gambler.