He unrequitedly loved Anna; Anna unrequitedly loved Marco; Marco probably unrequitedly loved some rando none of them had ever met. The world was pitiless. Nobody had any power over anyone else.
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.