Call me crazy, insane, weird, or whatever, but when I first read about Sebastian in CoG, I completely thought either Clary was going to end up with him instead of Jace (not that I
want that to happen, I was just so mad at Jace at the time for being an ass), or that Alec was going to end up with Sebastian, and Magnus would get mad because he's in love with Alec, and then Magnus would somehow use the White book to punish Alec and Sebastian (like, turning them into some horrible creatures). Then, Jace would go save them and Magnus would be put in a cell at the Guard, Alec would realize he only went with Sebastian because he was afraid of committing himself to Magnus, go save Magnus, and then they would be together. Though, Sebastian would want revenge then, because he really was in love with Alec, and Jace would be angry and confused, because Alec saved Magnus even though of what Magnus did to him, so Jace and Sebastian would think Magnus put a spell on Alec, so they would team up to try and save Alec, but then they themselves would fall in love. Then Clary and Simon would end up together one way or another. So basically it would end up that Clary and Simon are together, Jace and Sebastian, and Magnus and Alec. Isabelle would be the only one left, would get angry, and somehow destroy everyone's happiness, looking fabulous the entire time.

But, that was just my theory untill I read that Sebastian is a spy for Valentine. After that, there is no way that was happening. I'm just as happy now, though, because now Jace and Clary might get together

I'm only on page 302, and can't wait to read more

!!!