That's why its never a good decision to finance them knowing that their activities done is so risky to participate and if they lose for sure they might get broke then struggle financially, that's why our chance to get paid for what we lend to them is so slim. So to avoid any problem related to this stuff much better if we should not let them borrow our money and give them good advice regarding on financing and their poor gambling activity since for sure it can help them more rather than allowing them to do what those things can destroy them.
We should consider all conditions since if we just let them do what they want for sure they might think about that we are still fine and its ok that they would not pay because we still have money base on their observation.
We can tell them that we also need the money to meet our family's daily needs so we don't have enough funds because we will use the remaining funds as reserve funds for urgent matters. If they don't want to understand our reasons, then let's just let them be because that's the reality and we also don't let our family need their money more than they only need it for gambling.
Even though he says that he will definitely win, that is not a guarantee that he will win because his goal is only to get money from us for gambling. We should choose our family over that friend because if he is truly a good friend, he will definitely not impose his will on us. He will definitely understand what happened to our family and will look for someone else who is willing to fund his gambling.