The video doesn't show a real wedding, it shows the "groom's" mind.
The man knows his wife is cheating, the waiter and bridesmaid symbolize other people who obviously know this girl is a "whore."
brendan urie plays the mans conscience. He is telling the man to come to his senses, by showing him how much of a circus his relationship to the woman is. When urie and the circus come in, she is the only one who is truly worried, because she knows the truth. At the end, the man realizes that she doesn't love him and he should move on. This is symbolized by him and his consciense becoming one again at the end of the video and we see the man is happy.