I think he's jealous.

“When he saw her, he wanted to be with her; when he was with her, he ached to to…”

“Has there ever been an Inquisitor who didn't die a horrible death?" Simon wonde…”

“Do you remember, the night of the battle on Valentine's ship, when I needed som…”

“Something inside Clary cracked and broke, and words came pouring out. 'What do …”