This is what I think it means:
I think Mr. Brightside is like the explantion of Jenny Was a Friend of Mine (the song before Mr.Brightside on the cd) In Jenny it's about a guy who kills his girlfriend or maybe his best friend and then the cops get him and question him, and after that he has to go to jail. Mr. Brightside starts with "I'm coming out of my cage", so I think that now he's out of jail and sees all the things that have happened and changed since he stayed in jail. So he starts with telling about that he was doing fine with her but then she gets more distant of him because he is becoming arrogant ("because I want It all") So he sees her kissing someone else and then he asks himself "how it could end up like this" but he just doesn't want to admit that things are "falling apart" between them. Then he sees the girl leaving with the other guy and he is starting to get really jealous. Now he just pretends he didn't see anything and then the next time he sees her (Jenny was a friend of mine), they have a fight because of what he saw and she gets angry and the jealousy comes up again and he kills her. I think this, but now please tell me what do you think "Mr. Brightside" song means?
