Find That Book

Can’t find this book and it’s driving me insane. Believe I read it about 5 years ago in a library. What I remember is it’s a teenage boy maybe on holiday by the sea Andrew it switches between being narrated by him and a girl who lives there. He meets her at the beach and her distinguishing feature is the fact she smokes cigarettes and wears bright red lipstick. The girls unhappy with her life and convinced him to run away and somewhere along the way they join a circus. I think after time the boy gets jealous because she falls in love with one of the performers. There’s a conflict and all I remember is at the end they have to perform a magical/superstisous ceremony in a dark room with mirrors??? To release someone?? It’s driving me mad!