This is a thoug place to be. He will only change if he is willing to change. You can not and must not try to change someone’s behaviour. He will not admit that he stomach pain is from the poker playing, but that is because he is an active addict. I’am also a compulsive gambler myself.
So all the actions has to come from his side and his side only. Of course you can support him but ultimately he is accountable for his own actions.
My best advice would be to safeguard your financial position and go in a damage control mode.
The “allowed” gambling has to stop. As someone once said here ” gambling is like a mistress, staying close friends does not work” but he is the only one who can stop and that can only happens if he admits to himself that a little gambling isn’t right.