It's a complicated issue when you want to give advice for his own good, but he won't listen, and sometimes there will be aggression towards you. Well, for me, if he isn't asking for help, I won't talk about it too deeply. If he wants to ruin his life, I'm afraid there is nothing you can do about it. Why should we care so much about our friend? It's his privacy after all. But in case you really want to help, tell his family about his problem and ask them to keep silent. Only his wife, son, parents, can talk to him.
Maybe I won't care what other people do, but not with my best friend whom I have considered a brother. But what I'm thinking right now is how to convey it without destroying the friendship that has existed since childhood, and honestly its emotional nature makes me have to think twice about conveying it without causing other problems.
You're in a very difficult position here, and the right thing to do would be to try and convince your friend to visit a psychiatrist. However, I don't know how bad things are with his addiction, but if it's severe there is a risk that he will be very mad, break the friendship, and won't even listen to your advice.
In such a case you need to come very carefully, don't make any straight approaches. I can share my experience of what I did when my friend was an addict (only not gambling, but alcohol), but the psychology is the same here.
First, you need to take his side, make him see that you're in the same team he is. SO, you'd have to start gambling, share your experience (only be cautious not to become addicted yourself!), gamble together.
Then you'd need to
slowly start exposing some problems. E.g. say that you're facing financial troubles because of gambling (even if it's not true), can't stop thinking about it and then very gradually name all the problems that your friend is facing but as if they're yours. But don't make any hints or references that he might be having the same problems, that will ruin everything! He'll need to reflect that on himself and see that he's in trouble himself but through watching you.
So, the main psychology here is that the person often can't see when he is in trouble, but he can see it in others. But don't make it fast, or he'll suspect something, maybe make it weeks. Eventually, he will see the problem, and then and only then (if he doesn't think of that himself at that point) you can start talking about the psychiatrist.
That worked for my friend, and I gave that advice to other people that were in similar situations, it
always works if you do it right.
I hope this will help!