It always came at the time when she was least expecting it. At the worst possible moment, when she had a boyfriend or was on her way to having a boyfriend, when she would look at him one day and dammit, I like Jace. Again.
She would notice his hair and his eyes and his smile, his muscles and his marks, chasing each other around his body, and she wondered what other marks he had, hidden underneath his clothes, in places she wasn't allowed to see. She would laugh louder at his jokes and would feel a twinge of guilt when Alec looked at her with knowing eyes.
She never followed through with her feelings, whether because she was afraid he would, or because she was afraid he wouldn't, she never could tell.
My keyboard is completely messed up, so if there are any terrible spelling mistakes, I apologize.