Clary checks her phone, like three times in the same scene, because maybe Simon will forgive her and take her back. Clary is supposed to know Simon better than anyone else. Yet she seriously believes that Simon will forgive her that quickly? I mean, it’s been less than an hour since she passionately kissed her brother in front of him.
I mean it’s one thing for Simon to practically call her a whore for kissing a guy, she was interested in when they weren’t together. However, they are both now in a relationship and Clary has just made-out with her own brother right in front of him. Yeah I know that it wasn’t all her fault, but it really made it clear to everyone that you are really in love with Jace, and Simon was just a rebound.
I would feel sorry for Simon, but to be completely honest, he brought this on himself. He announced to everyone, without checking with Clary first, that they were in a romantic relationship by calling Clary his girlfriend. He was oblivious or deliberating ignoring every sign from Clary that she didn’t care about him. Simon has outright said that he is entitled to a romantic relationship with Clary because unlike Jace he was the one to put in the years of
work friendship, and therefore, had a right to her romantic interest over anyone else.
Honestly, as I said earlier, their romantic relationship was always meant to end this way In the end, Clary and Simon are both better off without each other.