It's not just gambling alone; what you said is true. When someone is excited, they can make huge promises to anyone. In this life, we should just learn not to put interest in the promises of someone if not we will get disappointed. What you can do is not say a word to him about the money, just let everything be and be his friend as usual.
If your friend had lost in his bet. You will notice he would stick to you for you to show compassion for him. Funny enough money won in gambling does not last forever, he will spend it all someday and then come back to you.
Money is an amplifier of ones nature, if one is the selfish type with money, when it comes to them, they will definitely going to be selfish when it comes. Gamblers shouldn't put in too much trust in what was promised to them especially if they are dealing with a gamblers. Humans act differently when we touch money, even the closest person you know can have a change of character when they make a certain amount of money. They said money is the only thing that can come between brothers. Which is true.
Money is everything and people do definitely be doing fight against other people even if it means on whatever the things that they've been that dealing into. It could changed up someones character, personality or treatment or even trying out to change that respect and thats how powerful money is and thats a fact. Talking about before and after on doing gambling on which on the moment that you've been that befor doing gambling then you will be having those thinking that you should be that doing just for the sake of fun on which it did happen and on the time that you made out some winning then experiencing a series of loses then you will be starting out to catch up those loses that you had made and since you've been that saying earlier that you do only play for fun then it should be just that fine. Yes, this is the way you should be that treating up gambling but usually people do made out some regrets at the time that they've seen that theyre profitable but didnt cash out on the right time.