Don't tolerate your friend by lending him money. It's going to be your daily problem if you have allowed that. But that's good that you have never given him any loan for him to gamble. Well, at least for him he's honest that he told you where he'll use the money. It's rare to see gamblers telling you the actual reason why they're borrowing money.
Now the question remain that Is it good to take loan to gamble?
No.
As you can see, the majority here is telling you that it is never good to take a loan for someone to gamble. If your friend isn't listening to you, just let him do whatever he want. But on your part as a good friend, you didn't tolerated him and already told him a good advise.