That's a big no-no. Gambling with another person's money is a great way to lose that person's trust and friendship.
If you didn't know when a person is addicted to gambling friendship doesn't matter to him, he cares more about making more and more profit and try to recover his loss. Borrowing money for gambling is literally the last thing a gambler should do and if he reaches such a stage the only way to remove him from gambling is by putting him in jail