What I took away from this experience is how the mentality of gamblers can change after a win. The thrill of success often leaves us wanting more and in this case it seemed like my friend was caught in that cycle, as I was feeling before too and he was unable to honor his word probably because he wanted to keep increasing his gains and bet more. It's a reminder that the brain is never truly satisfied when gambling, there's always the desire for more. I believe that friend deserves an advice, but I don’t want to embarrass him myself, is there a good way to talk to him without making him feel that Im indirectly asking him for the money he promised me?
It is similar to what happens to the brain of traders when they are having a good luck rush and they can feel the money coming their way, they just want to have more and more because of the huge amount of greed invades their body and mind.
In my opinion, if you actually consider that person to be a genuine friend, you should have a heart-to-heart and make clear you don't actually are pressuring him to give you some money out of what he promised, you don't even need directly to approach him, you could send him a text message clearing up the situation.
In the end, it is very sad when a long standing friendship gets spoiled because some money or a broken promise because of greed.
It is easy to promise money one does not have to begin with, but once money reaches ones hands, it is more difficult to let him go.
Hopefully he does not become addicted to gambling in the same way you used to, though.