Jealousy

Last month, the woman I'm seeing was in another city. She was out with her "friends" at some quiz pub or something, while I sat at home feeling jealous and down. That made me start thinking about jealousy and wanting to understand the mechanics behind it. I watched videos, read posts, and even started a book. To clear things up for myself, I decided to write about it. The main question I'm trying to answer is: what exactly bothers me when my girlfriend goes out with her friends? Or, more broadly, what am I really jealous of? The first thing that comes to mind is the possibility that some of those "friends" are more than just friends. I can even think of a couple of my girl "friends" from work who are a bit different from regular friends. We didn't have sex or anything, but there's definitely some tension between us. I'm not saying we're in love or that anything will happen, but I wouldn't want my girlfriend hanging out with thos...