As you may already know, he didn't leave the band because he wanted. It was Mana who kicked him out (or so I've heard). Anyway, I think I know how it happened. Mana called for a meeting only with the other 4 band members and called a vote to kick Gackt out of the band. OFC Gackt refused so the score was 1 (for kicking Gackt out of da band) -1 (for lettin him stay in da band). Yu~ki voted to kick Gackt out because as you know the least amount of photos in which only two members of Malice Mizer appeared togheter and in which one of em was Gackt was Gackt and Yu~ki. And Yu~ki motivated that Gackt didn't even give a shit about him. Most of times he didn't even say hi to him when the band members met (for making music or whatever other reason). Kami voted Gackt to stay since they were very close friends. And then Mana told Közi: It's your turn to decide, will Gackt stay in or will he get out? And Közi was like: You know Gackt, I like you, you are a great vocalist but I'm afraid I will have to go with Mana on this one since I've known him for a longer time than I've known you and besides he's the leader. And Gackt was like: After all I've done for you, FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU.