Complex sentence: By the mid- 1970s, the singer had begun an affair with a male American record executive at Elektra Records, and in December 1976, Mercury told Austin of his sexuality, which ended their romantic relationship.
Split into simpler sentences: By the mid- 1970s, the singer had begun an affair with a male American record executive at Elektra Records, which resulted in the end of his relationship with Austin. In December 1976, Mercury told Austin of his sexuality, which ended their romantic relationship.