Complex sentence: He is the librettist and collaborator with the American composer Theodore Morrison of a new opera about Oscar Wilde, "Oscar", which was given its world premiere at The Santa Fe Opera during the Summer 2013 season.
Split into simpler sentences: He is the librettist and collaborator with the American composer Theodore Morrison of a new opera about Oscar Wilde, "Oscar". It is to be given its world premiere at The Santa Fe Opera during the Summer 2013 season.