There is nothing you need to do to talk to him just keep quiet and see if he will keep his promise and it should go without saying, if he has the mind and considers you as his friend he will give what has been promised before.
From the way OP narrated his friends action I don't think his friend would even regard him even if he gives him sometime because if he was a man of integrity he would have done what he promised, perhaps in other way round I think the OP should even be grateful that it happen that way because from that event he has been able to no the true nature of the person he called a friend, however in most cases how all this things normally end is when his friend will lavish all the money he has won that's when he would remember he had a friend, so I actually like the OP response to him because on this case silence is the best.
Yes, it can be concluded that his friend forgot him when he was on top and remembered his friend again when he was down, yes, OP should be grateful because with this he no longer needs to respond to his friend in any situation, he also has to act indifferent to his friend so that his friend also realizes his mistake.
For me, friends play a very important role in my life if something happens, one day I will definitely need their help, so as much as possible not to break off friendship just because of money.