There's a lot of things that we do in life to feel good. We play video games, go out drinking, watch TV, get some good food, or we might go online. All of these things are alright if you're alone, but they feel even better if you do them with other people, usually. Drinking alone? Pathetic. Drinking with friends? Party. Video gaming alone? Loser. Video gaming with friends? Fun as hell. That brings me to my next point: The reason that we have sex is to feel good. Because it does feel really fucking good. And like the other things, it's fine alone, although it has negative connotations in several cultures (ya bloody wanker!). However, unlike the other things, it's mostly off-limits to do with whomever you please. When I've been in relationships, my girlfriend didn't care if I would go out and smoke a joint and just hang out with my bros. But she probably would have been pissed as hell if I fucked another chick. But why is this? I could play video games with my friends and it didn't mean that I love her any less because I'm doing it with others. Sex with others, on the other hand, could mean the end of a relationship. I'm not saying that people should just go around fucking everyone and everything. But I'm just wondering; why does sex mean so much to some shallow people when it has the same function as other recreational activities? It doesn't really make sense to me at all. TL;DR: Why do chicks get upset if you fuck other chicks?