Clary tried to hide her plan but she knew that people were suspicious of her. It wasn't just Max either, it was everyone who knew her. They had realised how shifty she was being and as much as she tried to hide her heartbreak it was evident that she was not okay, she needed to do it quickly.

The day she left numerous things happened, she wrote everyone a goodbye and thank you not, told her parents she loved them and spent a good portion of the day with Max. The most surprising thing was when she kissed Jace, she had stormed over to him whilst he was training, grabbed him and kissed him. She figured it was a now or never moment considering Valentine would probably kill her. When he pulled away she smiled and sauntered out of the room. She then spent the rest of the day hiding from him, she could have no reason to stay.

Clary was feeling pretty great about being able to leave, that was until Alec caught her.
"So this was your plan? Get home and go back to Valentine?" she looked at him stunned.
"I thought you said you never wanted to see him again?" Alec asked confused
"I… uh…" she knew that if she let Alec talk she would never be able to leave.
"Look… he needed Intel… he's my master" she cringed slightly. Alec looked at her thoughtfully, he wanted to hate her he really did, she took Jace but he couldn't. She was the most selfless person he knew at the moment.
"He's blackmailing you?" he guessed. Clary felt a traitorous tear run down her face.

"I'm sorry" she inched closer to her portal, Alec reached out to her.
"We can protect you" he promised. Clary shook her head wildly.
"No you can't Alec, you can't because I am the only reason that Max is in danger." Alec tried to dissuade her but before he could she jumped through the portal, Alec being reckless did the same.

The institute was not happy, not only had they lost their only leverage against Valentine and Sebastian, they had lost Alec. Jace was not happy that he had let the love of his life and his parabatai slip through his finger.
"I'm going to kill that bastard"
"We are not going to kill Valentine just yet" Izzy said
"Not him, Alec and then when I'm done with him I'm going to kill Clary. Why do two of the closet people to me have to be so self-sacrificing?" Izzy would laugh if the situation wasn't so serious.
"We'll find them Jace" she tried to be reassuring but deep down she knew that it was unlikely. She must wished that if they do find them that they will still be alive.