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?
If he is avoiding you already, I feel the best thing for you to do is to completely ignore him too, possibly he will definitely come around probably after he had squandered and gambled all the profit he made from that win away.
Any move you make now to approach him, he is definitely going to assume your coming around is simply to get your 10% from him, and he will possibly confirm this feeling the more if you try to advice him, like you said, he is surely going to assume that you are indirectly asking for the 10%, so for me, the best thing to do is to leave him alone, allow him live his life and only advice him when ever he himself decides to come around you again.