Complex sentence: In 1985, shortly after the founding of the opera company some of his students became concerned that he was spending too much time on this, he concurred, and withdrew as teacher to devote himself to music full time.
Split into simpler sentences: In 1985, shortly after the founding of the opera company, some of his students became concerned that he was spending too much time on this. He agreed, and withdrew his position as teacher to devote himself to music full time.