Alec would have said he could have benefited from a bit more in the way of constructive cowardice.

You have something on your neck," he observed.
Alec's hand flew to his throat. "What?"
"Looks like a bite mark," said Jace. "What have you been doing all day, anyway?"
"Nothing." Beet red, his hand still clamped to his neck, Alec started down the corridor. Jace followed him. "I went walking in the park. Tried to clear my head."
"And ran into a vampire?"
"What? No! I fell."
"On your neck?

You don't believe me?" Jace asked. "Fine. Go ahead. Kiss me right now."
Alec stared at him in horror.
"Exactly. Despite my staggering good lucks, you actually don't like me that way.

I did not make a pie,” Alec repeated, gesturing expressively with one hand, “for three reasons. One, because I do not have any pie ingredients. Two, because I don’t actually
know how to make a pie.”
He paused, clearly waiting.
Removing his sword and leaning it against the cave wall, Jace said warily, “And three?”
“Because I am not your bitch,” Alec said, clearly pleased with himself.

A parabatai. Like he was. And Jace knew, too, what that faded rune meant: a parabatai whose other half was dead. He felt his sympathy leap toward Brother Zachariah, as he imagined himself without Alec, with only that faded rune to remind him where once he had been bonded to someone who knew all the best and worst parts of his soul.

Alec was very still for a moment, barely breathing. Then, to Jace's surprise, he reached out and ruffled Jace's hair, the way an older brother might ruffle his younger sibling's hair. His smile was cautious, but it was full of real affection. "Thanks for seeing me," he said, and walked off down the tunnel.