I have the feeling that Blair will get stood up in the altar and not Louis. That’s the reason she run away and hide from everybody. And that Louis tell Blair that he knows she was going to run away with Chuck and that he can not marry her. 

Maybe Chuck told Louis about it, as his last chance to stop the wedding… and that’s why Ed says he is not using the best methods to get Blair back. 

I guess Dan will be the one that will help her to run away and that’s why Blair is using a hoodie… obviously  Dan’s hoodie :D