Complex sentence: Although Stefan got on well with the members of the band, he had other musical preferences; as a result, he chose to leave Helloween after the Rabbits on the Run Tour in early 2005.
Split into simpler sentences: Although Stefan got on well with the members of the band, he had other musical preferences. As a result, he chose to leave Helloween after the Rabbits on the Run Tour in early 2005.