Exactly. It's a strange dynamic, because when they were in a relationship Serena moulded herself to fit Dan's ideal, yet when Serena says "jump" Dan asks "how high?"
They put each other on a pedestal, he gets pissy that she can't live up to the ideal within his head, she feels trapped so she lies, he resents that he is being lied to, and the cycle starts all over again. Dan doesn't deserve to be consistently lied to because his girlfriend has a pathological problem facing confrontation, and Serena doesn't need to be made to feel that she is never good enough for him.
IAWE. I'm kind of wondering if Serena's re-discovery of her feelings isn't so much about Dan as that when they were together she had a clearer idea of what she needed to do/be to be better. Being directionless has been a hug part of her story since S3. Her romantic relationships are more a symptom of this than a cause or cure. I feel if they were to be serious about them at this point of the plot the whole Inside movie thing wouldn't have ended quickly with them falling into the above pattern. Their relationship also happened at the least cynical moment in her life, so if you subscript to the "Serene is really the most cynical of the mains" theory it is important The way the "Diamonds Are a Girl's Best Friend" dream sequence plays this up to its logical extreme.
The post S2 reactivations of this relationship have been very plot based and did not serve the characters well. I don't think the writers planned it in late S3 to prop Dair, but I do think they did to prop Juliet/Ben (the first part of the plot would not have worked if Serena wasn't desired by two main men and resented by two exiting main women). I still think for the most part S4 Dair was a chem test rather than a well thought out plot. (Considering that the Thorpe vs. Bass story was one of the planned out ones, I kind of wish more of the plots were experiments rather than well planned).