I can loan him in one condition he needs to be sober and stop gambling for at least a month to show that he is not using the money for gambling and it will be under close monitoring and supervision.
Its hard to grant a loan to anyone who is deep into gambling even if you are close to him or you owe him something, lending him will just give him money and reason to continue gambling in the hope that they can get all their losses back.
If he borrows money from you and gambles, you may not give him a loan later, but at that moment you cannot do anything to him. And you can never always keep an eye on a gambler, what he is doing or not doing. When a person borrows money, no matter what decision is given to him, he will take all the decisions in his head because he needs the money at that time. However, I think that instead of giving a loan to a gambler, you should stand by him or his family by buying him food or clothes because if you give money to a gambler, he will gamble, it is 100% sure.
There are some people in my area who come to me to borrow money, but I don't give them money. They come to me to borrow money in a way that doesn't show their need, like their daughter's education, but I buy everything they need for their daughter's education, but I don't lend them money because I know that person will gamble with the money.