Hi Rizqia
Great subject to research. The best book (in my view) on JM Barrie, his relationship with the Llewelyn Davies boys and the genesis of Peter Pan is Andrew Birkin's JM Barrie and the Lost Boys published by Yale University Press. There is also a biography by Lisa Chaney, Hide-and-Seek with Angels, a Life of JM Barrie published by Arrow Books (paperback) or Hutchinson (hardback), which is OK. There are many books on Barrie on the market but I believe these are the best and are easily obtainable online. Good luck with your studies and research.