Perfect Pretty Little Liars by Sara Shepard

Perfect is the third book of Pretty Little Liars, a series of young adult novels by Sara Shepard.
Now homeless, Aria goes live with her new boyfriend, Sean Ackard. Still seeing Ezra, their relationship is broken up when Sean informs the police, having found out the secret from "A". Emily plans to go to the police to stop "A", which leads to "A" taking revenge by outing her to the whole school. Emily's parents threaten to send her away if she does attend a "de-gaying" program, however, Emily realizes she can't change who she is. Spencer is nominated for a Golden Orchid Award for the essay she plagiarized, which "A" threatens to expose. Spencer comes to believe she might have killed Alison after discovering she suffers from rage-induced blackouts. Emily is in a secret lesbian relationship with her new neighbor, Maya, as Spencer has flashbacks to the night of Ali's death. Aria tries to keep her father Bryon's affair a secret from her mother and brother while Hanna deals with her social downturn by resuming her bulimia. Spencer remembers pushing Ali into a stone wall after a heated argument, and fears that she is the one who killed her. After Aria ignores "A's" threats, "A" reveals her father's affair to her mother, who kicks Aria out of the house.
Hanna and Mona grow apart and Hanna becomes involved with an unpopular boy named Lucas. After getting humiliated at Mona's birthday party, Hanna receives a text from A and recognizes the number. She intends to reveal the true identity of "A" to the other girls, but is run down by "A" before she can do so... (Summary by Wikipedia)