Even if your friend is rich and let you gamble his money. I think it's still not a good idea to gamble with money involved. I have an experience when we gamble with my friends and win like from 1 dollar to 100 dollars. Then he bet all of the money because he thinks it's a good idea like he get greedy, yeah you know the results we lost and things went awkward because I don't know what to say to him when he lost the bet.
Still the best to gamble with your own money, you can still gamble with your friends though its fun.