Given how little contact Ted had now with actual Anna, it was like he was in a relationship with an imaginary friend.
For the first time, Ted imagined fucking Anna the way he (almost) fucked Rachel: cruelly, without concern for her comfort, fully acknowledging that as much as he loved her, he hated her, too.
Ted was wildly uncomfortable. He wasn't quite sure who Rachel was on a date with, but it didn't seem to be him. He'd contributed nothing to the outing; as far as he could tell, she could have brought an inflatable doll with her to the movie and had an equally good time.