Gambling is worth playing if you are aiming for entertainment and nothing more but if you are aiming for profits then its a different story hence its really impossible to make stable profits on gambling and you would always end up broke on the long run. In your situation convince your friend to stop gambling immediately before its too late.
I think no one can stop you from gambling whether its friend or anyone, better self assessment is the best way to quit gambling and if someone is addicted so badly then obviously its not worth to gamble for him or her. My friends are there in real life where some actually bet for profit while some are having fun, they call me we watch sports and have part if he wins 