The same way OP showed the gambling universe to his friend, he can show a solution for gambling addiction. However, the final decision will be always on his friend's hands. The same way he started gambling because he wished, he will just start looking for treatment if he wishes genuinely from his heart. I don't blame OP for having introduced his friend to gambling, because he didn't force anyone into something they didn't want to do, therefore he shouldn't feel guilty for that reason. He should do only what is on his reach to help his friend, but if the friend doesn't want to, I fear there is nothing else to be done by OP.
Here I really salute what OP is doing because he still wants to be responsible for a problem that actually OP shouldn't blame himself too much and take responsibility for his friend's addiction.
It's true what you said, it all depends on the intention of an addict himself whether he has the desire to recover or not because if he has a strong desire to recover then everything will be easier to overcome.
But unfortunately OP's friend has not been able to realize his mistake and wants to have the desire to recover before OP and his friend's wife start to cure gambling addiction as soon as possible.
Incidents like this are commonplace and indeed an addict will be able to realize his mistakes when he has lost more things.