Why do I get so angry when my girlfriend is around other boys?

The last thing you want is your girlfriend to feel restricted and fearful when you walk into the room seeing her talk to other guys. I can see how you felt bad after she apoligised to you.. Try communicating this with her, tell her that she shouldn't have apoligised, it's not her fault, it's just you feeling uncomfortable. You can then work on it together. You aren't a maniac, you're clearly very overprotective, and that's not always a bad thing. Just don't make a scene... Lets hope the worst is her laughing back at what a guys saying and nothing else.