So what is the appropriate reaction from Daniel? On two separate occasion she used him to get back at McKay. Should he have ignored his hormones and emotions and just said Cassie, “I get it, fukk my feelings, needs, and hormones. You use me, draw an artificial line, that you don’t let me know exists until god heat of the moment. And I’ll just accept it, and ignore how you made me feel and hold your hand, and tell you you’re ok, and not also a manipulative a$$hole like me.”
What I guess you miss, is he explicitly told her, in no uncertain terms, he liked her, and wanted to see her again, and they could hang out. He said, I believe, I REALLY LIKE YOU, in the upmost sincere voice. What the comment is, from my interpretation, is a small example of how men, esp. high school level can treat women. He's so nice, and so sweet, and so caring, until sex is withdrawn, then he lashes out, in the most hurtful way, revealing, that he never really liked her, it was all an act, to sleep with her. She is genuinely hurt by this, and reveals more about him than her. What it reveals is the fear that girls at that age, and throughout can develop that all the men are only truly interested in sex. And this behavior begins in high school, and continues on.
A TV show can be the most well written show there is and it's still gonna have situations that play out very TV-like. It's supposed to be entertainment. 
