I do not claim to be an expert, but at least I have a little experience.
The first thing I recommend you do is eliminate "extra" money. Determine things you need to save money to accomplish and that you have a strong desire to accomplish. This could be investing for retirement, getting married, buying a house, etc. Do not designate what you are calling "extra" money as money you need to put towards a goal.
I also recommend you join a local Gamblers Anonymous group if there is one.
If you still have a problem you should probably start seeing a therapist. In most areas there are therapists who specialize in gambling addiction.
In some places there are even inpatient facilities for treating gambling addiction.
Finally, if necessary, you can get someone else to manage your money so that you will not have access to money to take to the casino. I have done this for two people.