One thing you should know about humans and promises is that, it is easy to make promises for them when the dice have not roll in their favor, but when the Dice finally roll in their favor, they will act as if the have forgotten all that have been promised by them, playing along with them will only lead you into losing that your own percentage, so the best thing to do is that, you have to ask him for the 10% you both agreed on as your own expected percentage when and if he eventually wins, and now that he has won, you have to press home your demands for your 10percent, gambler are easily carried away with the excitement of winning in some cases and this could effect their emotions greatly so one need to constantly keep them in check to know and remind them what they need to do as long as promises and agreement is concerned.

And the earlier you do this the better for you because if you waste too much time on this demands, you know how gambler's behave very soon he may tell you that he have gambled away all the winnings and have nothing left to settle you of your 10 %, so delay is dangerous for you at this point in time and you need to act fast, unless you want to lose your entitlement at the end of the day.