Everyday my friend gambles with his money as same with his life and he always gambling throwing away his money for nothing but losing and the worth part of it is he owes me money

That's a messed up bro. Your friend shouldn't be borrowing money and not paying it becase he lost it in gambling. He should not borrow just to gamble with it. You should advice your friend to think about what he is doing.
Really messed up bro >.< i did i really did

but he said to me that if he wins he will give me 50% of his winning money and he will also treat me to a fast food all i can eat.. so i trust him

what should i do?
Next time what you need to do is don't ever lend money to your friend because he will just feed it on his addictions. Say to your friend to stop gambling if he couldnt even afford the money in the first place.