I (30M) found out that my brother (28M) was involved in my ex girlfriend's (29F) infidelity, and it's caused a massive family argument

**UPDATE** - So it turns out that my brother was actually in a relationship with my ex. He's been calling her his girlfriend for years, but he's always said it jokingly in a "fuck buddy" kind of way, but now he's admitted that they've been in a serious relationship. Not sure how i feel to be honest, other than pissed off. I've been through this with 3 ex girlfriends now, and this one was the worst one. It's not like I expect everyone to remain single forever, but it's hard to treat my brother as anything other than him betraying me. He was super apologetic, so he still has that in his favour, but yeah, I might have to take a break from him. Thanks for all the advice guys, it's been really helpful.<br><br>**<br><br>I'd first of all like to preface this with some background info. My parents are wealthy, and own several fast food restaurants. You wouldn't have heard of the brand unless you live in the country I'm in. My brother and I are the only children, and we're currently in our 30s. <br><br>Way back when my brother and I were kids, my parents opened up a large trust fund account for us, with the idea that we could spend the money however we wanted once we turned a certain age. We weren't given access to the money, but we could use some of it for specific purchases, like cars, houses, college tuition, etc. So, we never actually had the money in hand until we turned 25. By then, we both had careers, so we both used our money to invest in a few businesses, donate to charity, buy some luxuries, etc. <br><br>So my ex girlfriend and i have been dating for 8 years. Things were great for the first 4 years or so, but gradually things started to fall apart in the last 4 years. In the end, I found out she was cheating on me. <br><br>The person she was cheating on me with was someone who was an employee at one of my parent's restaurants. They were a restaurant manager, which is a fairly high position when it comes to our business. But I recognised this person, because it was one of my brother's friends from back in the day. They were part of his clique in high school, and he was often round our house. <br><br>I was so angry with my ex girlfriend, but I wasn't really angry at this other person. I mean, I don't condone cheating, but it's not my place to be angry at someone for sleeping with my ex. I can't control that. <br><br>My brother and I told our parents, who were absolutely furious. They immediately fired the person, but my brother wasn't happy with this decision. He said that he was the same as him, that he was a victim of circumstance, and that he shouldn't lose his career because of my ex's infidelity. This caused a massive argument between my parents and my brother. They didn't see it the way he did, and told him to essentially grow up. This caused my brother to essentially breach a rift between him and our parents. <br><br>My parents and brother haven't spoken in a couple of weeks, and I've been trying to stay out of it. But my brother has been badmouthing our parents to our other relatives and friends, which is really pissing me off. I feel like he's acting like a fucking child, and that this is all so stupid. I mean, our parents can't stand idly by and pretend that nothing happened. They should be angry, and they have every right to be. <br><br>So that's my dilemma. I feel like I've lost my brother because of this, but at the same time I side with my parents. My brother is just being stupid and immature. I don't know what to do, and I don't know how to get my family back together. I've tried starting a conversation with him, but he's not listening. Any advice?<br><br>tl;dr! My brother's friend cheated on me with my ex girlfriend, and now my parents have fired him and my brother is angry with them.