disloyalty

My brother started a small business and decided to include my two cousins in it. My brother worked hard he took a class and everything to learn before starting. These two cousins both werent working and they dropped out of college (they are 20 and my brother is 22). One cousin decided that he doesnt need my brother amd he can start his own small business using my brothers ideas. It mad me so pissed off and he proudly told me about it and told me to promise not to tell my brother. I said i never started this conversation with you nor am i promising anything. Im not going go back him up for going behind his friend/my brother who was trying to help him earn a life. After that, when i met my brother i asked how everything was going and i asked about that cousin. And my brother knew he was like hes doing his own thing now and i was like yea he told me that hes starting a business too. My brother doesnt care he is just focusing on his business. It just pissed me off how my cousin could do this. They have been best friends since childhood. I personally dont think anyone can win from cheating from someone else. I didnt say it to his face but maybe i should of. I just want to go off on that cousin but i know its no point!