Complex sentence: Matsumoto was brought in because of his work on the songs "Yuki no Hana" and "Tsuki no Shizuku", and because of the size of the project, Matsumoto brought in Yoshiki, a friend of his, to help.
Split into simpler sentences: Matsumoto was brought in because of his work on the songs "Yuki no Hana" and "Tsuki no Shizuku". Because of the size of the project, Matsumoto brought in Yoshiki, a friend of his, to help.