That's why it is very important for addicted people to keep them busy in some other activities to stop thinking about gambling.
There is actually some rehab that rehabiliate those who are addicted to it so you could always choose to do it yourself or to put him in some rehab though that wouldnt matter at all because to cure addiction of gambling, someone needs to suffer first and wake up from their dream. By suffering, I actually mean to lose ton of money from gambling