Gambling can be stopped with will power and self control. You do not need therapy combined with other treatments, simply act like a responsible adult.
Many have tried that but failed. There are stubborn gamblers who believe they can stop at any time, but they fail miserably. Those who say that they can stop their addiction to gambling are those people who deny that they are addicted to gambling, and it’s hard to cure these people.
Curing addiction starts with admitting that you need help to fight your addiction, because you are losing everything you value.
This is why there are s called groups like Gamblers Anonymous to help gamblers cure their addiction through group therapy with the help of professionals.