Jace would rather be anywhere else than here - stuck in some alternate dimension with Clary and Simon frigging Lewis. But, unfortunately, he doesn't have a choice. Also, Jace is not okay.

Clary has never been any good at putting things back together. When they were in middle school and she accidentally knocked over Simon’s Lego Millennium Falcon, he’d already known to say it was fine repeatedly and usher her out the door instead of accepting her offer to help him rebuild it; if he’d let her try, the wings would have ended up upside down and there suddenly wouldn't have been space for the engine. Her heart is in the right place, usually, but it doesn't often translate to her hands. So when he hears through the shadow world gossip mill that Alec's parabatai rune disappeared briefly, it doesn't take more than one look at Jace’s face to know that she’s been fucking around with the threads of fate again. And, well. She's never been that great at sewing, either.

Most nights they stay up later than they meant to, laughing. “It's like a slumber party every day,” Simon says, and Jace smirks and says, “I don't know what kind of slumber parties you went to,” and Maia says, “More than you. I thought Shadowhunters weren't allowed to have fun.”

The breakup starts with Magnus. Well, no, it doesn’t. The breakup starts when Alec finally says the words “I’m gay,” and Jace says “Okay?” and Alec looks at Magnus, out and proud, and happy, and he knows that he wants that. He wants to be able to hold hands, and kiss, and have sex without worrying about leaving hickeys where they might be seen. Or: Alec wants a public relationship. He can't do that with Jace, so they break up, not very cleanly. Magnus steps in, and then Jace gets jealous.