This is a deleted Jalec scene from City of Glass, where Jace kisses Alec to convince him that he’s not really in love with him.
“Drop it, Jace,” Alec said in a warning tone.
Jace was having none of being warned. “Magnus says it’s because you’re hung up on me. Is that true?”
There was a moment of utter silence. Then Alec gave a despairing howl of horror and put his hands up to cover his face. “I am going to kill Magnus. Kill him dead.”
“Don’t. He cares about you. He really does. I believe that,” Jace said, managing to sound only a little bit awkward. “Look. I don’t want to push you into anything, but do you maybe want to —”
“Call Magnus? Look, that’s a dead end, I know you’re trying to be helpful, but —”
“—kiss me?” Jace finished.