To me, Dan and Blair together always felt like a novel you read on an autumn day to warm you up. Chuck and Blair's yo-yo relationship is so bland when you look at it as a whole because it's the same storyline time and again (blair and chuck get together, blair and chuck get apart, chuck gets a new girlfriend, blair is mad but blair moves on, blair gets a new boyfriend. chuck suddenly wants her and so on). Most of the relationships in this show are dragged to the point of repetition and blandness. But I felt Dan and Blair's time was too short. And that's what makes it all the more bittersweet. Also, for me post season 5 Dan and Blair's relationship doesn't exist. It's like the writers have undone all their development not only relationship wise but also character wise.