I don’t think Will Herondale and a sense of responsibility are even on speaking terms

There might not be so much of a difference between the side of Light and the side of Dark as you suppose. After all, without the Dark, there is nothing for the light to burn away.

Will!" Charlotte threw up her hands. "Why didn't you say so?" "You know, the books on demon pox are in the library," Will said with an injured tone. "I wasn't preventing anyone from reading them

The moment the door opened, Jace seized up a yellow pencil lying on the desk and threw it. It sailed through the air and struck the wall just next to Luke's head, where it stuck, vibrating. Luke's eyes widened. Jace smiled faintly. "Sorry, I didn't realize it was you." ... Luke indicated Simon and Clary with a wave of his hand. "I brought some people to see you." Jace's eyes moved to them. They were as black as if they had been painted on. "Unfortunately," he said, "I only had the one pencil." -Jace & Luke, pg.43-

You know what the worst thing I can imagine is? Simon had said. Not trusting someone I love.

If you do not help me," Tessa said to Jem, "I swear, I will change into you, and I will lift him myself. And then everyone here will see what you look like in a dress." She fixed him with a look. "Do you understand?

If there is a life after this one, he said, let me meet you in it, James Carstairs.