It's already been one week since Constance learns of Darren's true nature. And the latter haven't been to school ever since his attempt to rape Constance. 

Him running away, actually means that he tried raping Constance and everything Jace told Constance about Darren is true. In anger, Constance burned the pink doll Darren gave her. She thought that the doll is a sign of friendship but it's nothing but a sign of deceit. Darren deceived her into trusting him. 

When she told Jocelyn more of what Darren did, like the things which Jace told her that Darren confessed to him— Jocelyn was more disappointed in Darren. She still can't believe...