Why Zayn Malik left direction

The 22 years old,  Zayn Malik has decided to quit the boyband, One Direction, leaving the remaining 4 boys ; Niall Horan, Harry Styles, Liam Payne and Louis Tomlinson. In a statement released by Zayn, he said : 

                             

    My life with One Direction has been more than I could ever have imagined.But, after five years, I feel like it is now the right time for me to leave the band. I'd like to apologise to the fans if I've let anyone down, but I have to do what feels right.

The other boys in the group will continue on their 5th album and also continue on their world tour. One direction said :

   We're really sad to see Zayn go, but we totally respect his decision and send him all our love for the future. The past five years have been beyond amazing, we've gone through so much together, so we will always be friends. The four of us will now continue. We're looking forward to recording the new album and seeing all the fans on the next stage of the world tour.