Dean's first thought was to push Jo away. He by passed that and instead turned his face so that her kiss caught his lips. His eyes fluttered. He should push her away, and walk out, because it was exactly this kind of behavior that was getting them all in trouble.
Sex with Anna was supposed to be just sex. Sex with Cas was never supposed to happen, and it didn't. But Dean had kissed Cas, and the end result was the same. Tossed out on his ear. Sex with Jo was a bad idea for a number of reasons, and yet Dean wasn't pushing her away.