Complex sentence: The cathedral is the seat of the Greek Orthodox Bishop of Boston, and served as the headquarters of the Greek Orthodox Metropolis of Boston until c.1973, when it was moved to 162 Goddard Avenue, Brookline, Massachusetts.
Split into simpler sentences: The cathedral is the seat of the Greek Orthodox Bishop of Boston. The headquarters of the Greek Orthodox Metropolis of Boston are at 162 Goddard Avenue, Brookline, Massachusetts.