You're my sister," he said finally. "My sister, my blood, my family. I should want to protect you"—he laughed soundlessly without any humor—"to protect you from the sort of boys who want to do with you exactly what I want to do."
Clary's breath caught. "You said you just wanted to be my brother from now on."
"I lied," he said. "Demons lie, Clary. You know, there are some kinds of wounds you can get when you're a Shadowhunter—internal injuries from demon poison. You don't even know what's wrong with you, but you're bleeding to death slowly inside. That's what it's like, just being your brother."
"I had to try. And I did." His voice was lifeless. "But God knows, I don't want anyone but you. I don't even want to want anyone but you." He reached out, trailed his fingers lightly through her hair, fingertips brushing her cheek. "Now at least I know why."
Clary's voice had sunk to a whisper. "I don't want anyone but you, either.
Romantic Quotes And Sayings by Cassandra Clare, City of Glass