I can't attempt Cassandra Clare's perfect writing, but I do have my own ideas.
"Why lie" Mark had said days before. She had tried to believe it, really tried.
Now that she understood her parents death there seemed to be a hole in her. She had spent hours every day and hours a week searching for clues. It had never left her mind. Now there was a void.
At first she had thought that all her energy could go into Mark. Grooming Mark and her to be the perfect couple, but it wasn't working.
Mark genuinely did like Emma. At one point he had even loved Emma. He remembered the Dark War, telling Julian to stay with Emma. It's because he thought she was gorgeous. She was strong and had a great sense of humor. She needed someone.
But at the end of the day Mark and Emma weren't good together. They had spent a large portion of the last few days trying to make it seem as though they were.
Emma had devised a small strategy. The first day they sat together for breakfast, they laughed at each other even though Mark hadn't played into her sarcasm very well. Julian tried to spend time with Emma, but she always came up with an excuse involving Mark.
During dinner she had instructed Mark to periodically brush hands with her.
That might she had made sure Mark stayed in her bedroom well into the night. Even if all they were doing was reading, Julian didn't need to know that.
The second day Emma and Mark had babysat Tavvy and looked after the others while Julian attended to Arthur and the Institutes business.
"Emma, may I speak to you," Julian called from the kitchen.
"Yes," She followed him out. Acting clueless to what he might be wanting to say. But she really knew, she spoke "might not want to leave Mark in there alone too long. Remember what happened-"
He cut her off, shaking his head, "What are you doing? Do you think having a fling with Mark is going to get us out of your head. Emma I know you and I know what you are doing."
Emma shook her head slightly, hoping she could pull this off. She had never been the best liar, but this had to be believable, "Jules, what are you talking about? Me and Mark, no, I never even thought. I mean he's back for good and I missed him is all."
"Your sure your not trying to start something. I've seen try to do this before."
"Never, he's your brother after all," She said unconvincingly on purpose. If you and Mark ever... I wouldn't be able to come back from that.
"Okay, good to know," He reached her hand and squeezed it, then turned in the direction of the attic. The moment their skin had collided her heart fluttered with guilt from what she was doing to him, but she shoved it down.
Emma realized she had been holding her breath. She turned to go into the kitchen, but chose to ascend the stairs instead.
The only thing left in her closet was one picture. Her mom and dad at their wedding. She sat cross legged and shoved the door shut.
"This was supposed to be better, get easier after I found the truth. But I only feel more conflicted... Mom I need you to tell me what to do."
She felt a knot form in her side. At first she jumped up, panic coursing through her. She thought he might be hurt.
It disappeared quickly. Then she felt an overwhelming urge to cry. These weren't her tears, she knew, this was from Julian. At that she was even more guilty for making him feel so terrible.
But she suppressed that quickly. It had only been two days, just because they were no longer physically connecting didn't mean their feelings had died any.
They were still together enough that they could feel each other's emotions. For that, Emma had to be careful. If he could sense how terrible she felt then he would never give up.
At times Emma wanted to give up, but what Jem had said scared her. She had to protect Julian, always.
Right now Julian didn't understand what to feel. He had felt upset, mad, a burning rage at the thought of Mark and Emma together. But halfway up the stairs he paused.
He was tired he had hardly gotten any sleep in months. Between the kids, Malcom, his feelings toward Emma, and his uncle it was all he could do to stand sometimes.
And now, now he didn't even have Emma. He had scared her away. Or she had run away. Either way he no longer had his best friend.
Julian didn't cry, he hadn't really cried in years. But it was over, he had one piece of his family back, there was no danger. For once he could relax. He did, he sobbed. He had always felt unhappy but in these few moments it had amplified. He felt like this dark weight on his shoulders was engulfing him. Pulling him under.
At least there was no where to go but up.