Let's not forget Serena screwing Nate. At least she wasn't actually dating Dan while him and Blair had a Thing . Serena is the bad friend.
Dan and Blair is an absolute disappointment, but it even furthers my hatred for this couple knowing about Dan and Serena's past. Blair is being a horrible friend and frankly, a horrible person. The best season of Gossip Girl so far is when Chuck and Blair were together. It's obvious that Blair and Chuck are meant to be and the rest is just ridiculous side story.