You have two good questions here that need answers. The best answer to the first question is that if you say that you will hide your envy and jealousy for the sake of peace, then you will be the victim because you will be affected. It is not easy to see your fellow friends win while you are losing, and hiding that feeling will be very hard to do. 
 
And for the second question, all you need is to continue going to the casino to get her with him, but instead of you playing differently, you might play the same game together rather than different games, and if it doesn’t still work, then you will be giving him the money that you want to gamble with. If he wins, then you collect your money together with the profit. To me, this is a simple thing because I will not stress myself anymore since gambling is a game of luck and I have a friend who is lucky, so it’s something to be happy about without being jealous or envious about the situation.